MeLEAGR IN'I D^:.] 



MUSEUM OF ANIMATED JS^ATURE. 



263 



contemplated, from the Pectinidae to the present, 

 are included by t'uvier tinder his great section Les 

 Ostraces; and liere, then, ends the Monomyariun 

 subdivision of it. 



The succeeding genera, belonging to the Ostracea, 

 and indeed, generally speaking, all the following 

 groups or families of Bivalve Moilusks, are Diniy- 

 urian, excepting Tridacna. 



DIMVARIA. 



Family MELEAGUINID.B (PEARL-OYSTERS, 



&c.). 



Under the comprehensive genus Avicula Cuvier 

 includes two sections: one, the Pearl Oysters, Mele- 

 agrina, Lam. (Margarita, Leach); and the restricted 

 genus Avicula, Lam., of which the Mytilus Hirundo 

 of Linnajus, a native of the Mediterranean, and the 

 Avicula raacioptera, are examples. 



To the genus Avicula Mr. Sovveiby also refers 

 the genus Meleagrina of Lamarck ;' regarding the 

 distinctions between them as of trivial importance. 

 The shell in both is foliaceous externally, and in- 

 ternally of a brilliant pearly lustre. The left-hand 

 valve is contracted and notched posteriorly, and so 

 is the right, but very slightly. Through the sinus 

 thus formed passes the byssus, by which the shells are 

 moored to rocks and stones. Theliganiental surface 

 is marginal and broadest in the centre; and there 

 is generally a small tooth in each valve near the 

 umbo. Generally this tooth is most conspicuous 

 in Avicula, but is not always found; whilst in 

 Meleatciina it is, on the other hand, often apparent, 

 though sometimes absent. The muscular impression 

 is nearly central, somewhat circular and large. 



.As thus characterized, Avicula will comprise two 

 sections, namely, one in which the species have the 

 hinge line considerably prolonged — Avicula of 

 Tjimarck ; the other comprising such species as 

 are without that prolongation— ^Meleagrina of 

 Lamarck. 



Cuvier thus defines Avicula (Les Arondes) : — 

 The shell has the valves equal, with a rectilinear 

 hinge, and is often carried out into wings; the 

 liijament is narrow and elungaled ; small dentilations 

 ollen appear on the hinge, on its anterior part ; and 

 belo.v the angle on the side near the mouth is the 

 notch for the byssus. The anterior adductor 

 muscle is still extremely minute.* Those species 

 are termed Pintadines (Meleagrinae) which have 

 the auricles but little salient. The term Avicula is 

 reserved for those in which the auricles are more 

 pointed and the shell is more oblique : they have 

 on the hinge before the ligament the vestige of 

 a tooth at least, of which scarcely any trace is per- 

 ceptible on the Pintadines. 



As the two so-called genera thus stand, it may 

 be at least convenient to consider them separately, 

 under a family title ; for even if it be deemed un- 

 philosophical to retain the two genera, still Avicula 

 seems to be the type of a family form. 



2899. — The Bboad-winoed Avicule 

 (Avicula macroptera). This shell, of which the 

 valves are represented open so as to display the 

 hinge, will convey a better idea of the general 

 characters of the genus than any verbal details. 

 These shells, as those also of the genus Meleagrina, 

 are natives of the warmer seas, where they moor 

 themselves at various depths to the surface of rocks, 

 old shells, and other submarine objects. 



2900.— Tub Fkahi.-Oystke 

 (Mekngn'na Martjnritifera). Mytilus Margariti- 

 feriis, Linn. ; Avicula Margaritifera, Soweiby. 



Our pictorial specimen of this interesting shell is 

 that of a younir, or at least not aged specimen ; it 

 is marked with beautitul foliations, which disappear 

 when the shell has attained to a large size. 



The valves are semicircular, greenish externally, 

 and lined internally with a layer of the most beau- 

 tiful nacre. From the size of the ornaments made 

 of this nacre, or mother-of-pearl, some idea of the 

 magnitude attained by the shell may be appre- 

 ciated. Were it only for the production of this article, 

 so much in request for all kinds of" bijouterie," this 

 shell would form an important object of commerce ; 

 but yielding as it does its nacreous lining in such 

 abundance and solidity, it affords also those more 

 valued nacreous drops or nodules called pearls, 

 estimated in the East, time immemorial, as " of great 

 price" — the ornaments ot kings. 



Pearls are procured in both hemispheres. In 

 the Old World, the Gulf of Persia, the west coast of 

 Ceylon, and the coast of Coromandel are the chief 

 pearl-stations. The Algerine coast and the Sooloo 

 islands also afford these treasures. 



In the New World, the neighbourhood of St. 

 Margarita, or Pearl Island, and other localities along 

 the coa.st of Columbia, are noted, and the Bay of 

 I anama also produces them. 'J'he fisheries on the 

 coast ot Columbia must indeed once have been 

 va.uable, for Seville alone is said to have imported 



* -M. l>c»liiyM •uiM Avicul« to he Monomjatiaa. 



upwards of 697 pounds in the course of the year 

 1587. Philip the Second's celebrated pearl, which 

 weighed 250 carats, and was valued at 150,000 

 dollars, came from St. Margarita. Yet the pearls 

 of the West are not to be compared with those of 

 the East in shape, beauty, colour, or texture. We 

 are not aware that any established fishery is now 

 conducted at St. Margarita, or on the coast of 

 Columbia on an extensive scale, after the failure of 

 the Columbia and Panama speculation in 182G. 



On the contrary, the pearl fisheries of the Gulf of 

 Persia, of Ceylon, and Coromandel are still actively 

 prosecuted durinir the appointed seasons. 



Cuvier, in his ' R(5gne Animal,' places in close con- 

 tact with Avicula and the Pearl-oysters the genus 

 Etheiia of Lamarck, and which writers regard as 

 belonj;ing to tlie Cliamidse. M. de Blainville, 

 M. Ueshayes, and Mr. Bioderip, however, all agree 

 that the EtheriiK ought to be separated from the 

 Chamidae ; and M. de Biaiiville considers them as 

 coming within the pale of the Margaritacea, or 

 family of pearl-oysters. 



Lamarck regarded the Etherise as oceanic, and 

 accounted for those shells having escaped the 

 notice of zoologists on the presuBlption that they 

 were attached to rocks at great depths. The first 

 conchologist who ventured to doubt this, and to 

 suspect them to be fluviatile, or at least tlie inha- 

 bitants of estuaries at the mouths of rivers, was 

 Mr. G. B. Sowerby ; his opinion has been confirmed 

 by M. Cailliaud, who was the first to make known 

 the fact that the genus is an inhabitant of fresh 

 waters. From M. Cailliaud's materials M.deFerussac 

 published a paper in the ' Menioires de laSocielfi 

 d'Histoire Naturelle,' vol. i., including a revision of 

 the species. 



M. Rang, during a voyage to Senegal, made some 

 interesting observations on the Etherise which live 

 200 leagues from the mouth of the river Senegal, 

 and, together with M. Cailliaud, who received the 

 animal from the Nile, published a memoir (' Me- 

 moires du Museum dHist. Nat.') replete with infor- 

 mation, in which the mollusk was for the first time 

 described. 



The livers of Africa and Madagascar appear to 

 have afforded all the specimens, still by no means 

 common in cabinets, which have hitherto been 

 collected. 



M. F.'russac gives the following information from 

 M. Cailliaud :— 



"We meet with Etherise," says that zealous 

 traveller, "after passing the first cataract, and they 

 do not appear to exist below ; they become very 

 abundant in the province of Rebata, and below the 

 peninsula of Meroe. The inhabitants collect them 

 on the banks of the river, to ornament their tombs 

 with them, and they say that they come from the 

 more elevated parts of the Nile, from Saida, where 

 they are eaten." M. Cailliaud found them as far as 

 Fazoql, the most distant country into which he 

 penetrated from the Blue River. 



In Sennaar the inhabitants informed M. Cailliaud 

 that during the summer season, when the river was 

 low, they took them with the animal ; but notwith- 

 standing all his endeavours, M. Cailliaud could not 

 obtain any living specimens, the river being then 

 always too high. They are said to be common in 

 the Jaboussi, a river which runs into the Blue River, 

 and in all appearance the numerous confluent 

 streams of this great arm of the Nile produce them 

 also. The number found upon the tombs throughout 

 Ethiopia is so great, that it is astonishing that Bruce 

 and Burckhardt should not have mentioned them. 

 (See ' Zool. Journ.', vol. i.) 



M. Deshayes, in his treatise on the genus, in the 

 ' Encyclopi'die Methodique,' states that individuals 

 of the same species adhere by the one or the other 

 valve indiff'erently, which is not the case either in 

 the oyster or the Chama;. The Cliamce, however, 

 as has been observed by Mr. Broderip, are found to 

 be attached sometimes by the right and sometimes 

 by the left valve. 



The shell of Elheria is characterized as thick, 

 nacreous, adherent, very irregular, unequivalve, 

 and inequilateral. The umbones are short, thick, 

 and indistinct; the hinge is toothless, irregular, 

 undulated, and callous; the ligament is longitudinal, 

 tortuous, external, and penetrates pointedly into the 

 interior of the shell. The muscular impressions are 

 oval and inegular ; pallial impression narrow and 

 small. 



The mollusk is described as closely resembling 

 unio. The lobes of the mantle are disunited and 

 without siphons. The mouth is rather large, with a 

 pair of palps, as in unio ; and, what is singular in 

 an animal which lives adherent to foreign sub- 

 stances, it is provided with a very large foot, which 

 may be compared, in regard of its form and position, 

 with that of unio. May not this large foot have 

 reference to the acquisition of food ? 



2901. — The Semilunate Ethebia 

 (Elheria semilunatu). The species of the genus 



Etheria are at present in some degree of uncertainty. 

 Lamarck records four : these M. Ferussac and M. 

 Deshayes reduce to two; and M. Rang considers 

 F^ Tubifera of Sowerby and E. Cailliaudii of 

 Ferussac as identical ; and E. Cortoni of Michelm 

 to be the same with E. Plumbea of F6russac. The 

 variation in the form of the shell from age and other 

 circumstances is so great, that were not this fact 

 kept in view, each individual might be regarded as 

 a distinct species. Even in the same species there 

 are individuals armed with spines and others devoid 

 of those appendages. 



Family MYTILID^ (MUSSELS, or Muscles). 



The family Mytilidae, as here restricted, is equi- 

 valent to the first section of Cuvier's great group, 

 which he terms Les Mytilaces ; that is, it includes 

 the genera MytiJus, Mo'diolas, and Lithodomus (Les 

 Monies propres of Cuvier), to -which we add the 

 genus Pinna, although avvare that the mantle has 

 no posterior commissure, and consequently no 

 siphon, and that Cuvier gives it as a typical form 

 under his Ostraceans. Yet its approximation to the 

 Mytilus cannot be overlooked, and if we are to attach 

 an over-great importance to the existence of siphons, 

 and their number, we must then establish Pinnae as 

 the type of a family in close contiguity to that of 

 the Mytili. Leaving this point open, let us first 

 direct our attention to the genus Mytilus, which 

 includes that well-known species the Edible Mussel 

 (M. edulis). 



The genus Mytilus is abundant on most rocky 

 coasts, where facilities are afforded for the species 

 mooring themselves to reefs, stones, and other sub- 

 stances covered at high water, but left dry by the 

 ebbing of the tide. To the byssus we have already 

 alluded, and explained its mode of production : 

 when the mussel is once moored, it does not, in the 

 opinion of Mr. G. B. Sowerby, habitually disengage 

 itself ; though he admits that when torn from its 

 anchorage by the force of the waves, it may live for 

 some time without being in any manner affixed. 

 It is not only on rocky shores that the mussel 

 abounds, we have seen beds of mussels on low, flat, 

 sandy, or pebbly shores, as for example on the low 

 coast between Southend andShoebuiy Point, Essex, 

 where they greatly abound : numbers, as we ob- 

 served, were totally free ; others had iheir byssus 

 attached to small shells, little pebbles, or fragments 

 of shells mixed with sand, small stones, and the 

 like ; and certainly whole strata of these shells 

 must in such situations suffer a greater or less 

 change of place with an ever-flowing and retiring 

 tide on a low flat shore left dry periodically over a 

 wide extent of surface. 



Of the figure and colour of the shell of the com- 

 mon mussel nothing need be said ; but, with respect 

 to the mollusk, few of the thousands who have 

 eaten it know anything beyond its flavour. In 

 form this mussel resembles that of its shell : the 

 lobes of the mantle, adherent at their edge to the 

 edge of the shell, are continued dorsally and open 

 in front, but are united posteriorly in a single point, 

 so as to form a short siphon, or orifice, for the pas- 

 sage of the egesta. The mouth, in a sort of hood 

 near the apex of the shell, is rather large, and 

 furnished with two pairs of soft palps, pointed, and 

 fixed by their summit only. The foot is slender, 

 cariying at its base and posteriorly to it a byssus, 

 known as the " beard." There are two adductor 

 muscles : one at the apical part of the valves, small ; 

 the other situated posteriorly, large and rounded. 

 Fig. 2902 exhibits the posterior part of the body of 

 the common mussel, displaying some of the prin- 

 cipal organs : A, right lobe of the mantle ; D, por- 

 tion of intestinal tube; G, branchiae; H, foot; J., 

 posterior muscle ; L, superior tube ; O, heart ; P, 

 ventricle ; Q, auricle ; X, pericardium ; b, tentacles ; 

 d, byssus; e, gland of the byssus; g, retractile 

 muscle of the foot ; /;, valves of the mantle ; i, egg 

 duct ; _;', excretory orifice ; k, internal ditto. 



Fig. 2903 shows the form of the eggs of the mussel, 

 magnified. 



Fig. 2904 shows the mussel lying in a detached 

 valve with the byssus ; the lobe of the mantle cover- 

 ing t he exposed surface is slightly contracted, showing 

 the branchiie. 



Fig. 2905 exhibits the mussel, as seen when the shell 

 is partially open ; the byssus maybe observed rising 

 from the root of the foot posteriorly ; the commissure 

 of the mantle bounds the view behind, and in the 

 space intermediate are the egg and excretory ducts, 

 pointing to the short siphon produced by the com- 

 missure, where the great adductor muscle is also 

 apparent. Figs. 2906, 2907, and 2008 also exhibit 

 the common mussel : Fig. 2906, the shell with the 

 valves closed and the byssus emerging ; Fig. 2907, 

 an internal view of oneofthe valves, showingthe mus- 

 cular impressions ; Fig. 2908, an external view of one 

 of the valves. The common mussel is known to pro- 

 duce minute pearis, called seed-pearls ; and we have 

 found two or three not unfrequently in a single shell. 

 We need not say that the mussel is gregarious, 



