270 



MUSEUM OF ANIMATED NATURE. 



[Ark-Shells. 



2934. — ^TtaE Niu Ibidixa 



{Iridina nilotKa, Sowerb.)- Spatha nilotica, Lea. 



We have already alluded to this species, which 

 M. Deshayes, in his last edition of Lamarck, makes 

 identical with Iridina exotica (.\noUonta exotica, 

 Blainv., and Le Mutel, Adanson), but from which 

 it is distinct. Accordini? to Ranjj the genus Iridina 

 belongs to the cockle family, Cardiacea, Cuvier, 

 Conchacea, De Blainville. 



To these forms are added others divided into — 

 Plicate shells. Nodulous shells, Smooth shells, and 

 Spinous shells. 



Plicate Shells. 



2935. — The Plicite Umo 

 (Uttio piiratus). This species is remarkable for the 

 waved elevations of the valves ; it is a handsome 

 species. 



Nodulous shells. 



2936.— The Pistclar Usio 

 (Unio pustulosiis). The somewhat rounded valves 

 of this shell are covered with pustular elevations. It 

 was fii-st described by Mr. Lea. 



: Smooth Shells. 



2937.— The Pdspi-e Uxio 



(Um'oprirpurms), Unio complanatus. This richly 



coloured Unio is a native of America. It was firet 



described by Say. 



Spinous Shells. 

 2938.— The Spi.sous Unio 

 (Unio spinosus). This species, first characterized 

 by Mr. Lea, appeal's to have been discovered by 

 Uartram, who found it in the Mississippi. It is 

 remarkable for the spines that rise abruptly from 

 the valves. 



VAfith respect to the arrangement proposed by 

 Mr. Lea, it appears to be completely artificial ; and 

 v?e agree with Mr. Swainson, who says that no per- 

 manent characters will be found to retain either the 

 genera Dipsas (Leach), Hyria (Lamarck), or Alas- 

 modonta (Say). Yet in the second series of his 

 'Zoological Observations' the same writer retains 

 as genera Unio, Hyria, Iridina, Anodon, and Alas- 

 modon. 



In the Naidse the foot is very large, and com- 

 pressed, almost quadrangular, and of consi- 

 derable mobility ; the mantle is garnished pos- 

 teriorly with little tentacles or filaments, and its 

 bottlers are free. 



It would appear that about three hundred and 

 twenty-three recent species are known. Mr. Lea 

 in his tables thus enumerates them : — 



Of the subgenus Unio. — Two hundred and thirty- 

 five specie?, and twenty which he has not been able 

 to admit as certain. Distribution — Europe, Asia, 

 Africa, North America, and New Holland, but by 

 far most abundant in North America. 



Subgenus Margaritana. — Twenty admitted, two 

 unknown. Distribution — Europe, North America, 

 South America, and perhaps Africa. 



Subgenus Dipsas. — Two recent, Asia. 



Subgenus Anodon. — Fifty-eight admitted ; seven 

 unknown to Mr. Lea. Distribution — Europe, 

 Africa, North America, South America, New Hol- 

 land. 



Subgenus Iridina. — Two recent ; Africa. 



Subgenus Spatha.— Six recent ; Africa and South 

 America. 



Numerous as are the recent species of Nai'dae, 

 there appears to be a great paucity of fossil forms. 

 Mr. Sowcrby, indeed, referring to Anodon in his 

 ' Genera,' says, that unless we are justified in con- 

 sidering the Bivalve from the Coal-Measures, 

 figured in the British mineralogy under the name of 

 Mytilus crassus, as an Anodon, he knows of no 

 fossil species. Subsequently in the same work he 

 refers many fossil shells found particularly in the 

 Coal-Measures to the genus Unio ; judging alone 

 from the casts of the inside, and comparing them 

 with recent species. 



Dr. Mantell, Professor Phillips, Mr. Lonsdale, 

 and Dr. Fitton record various species of Unio, from 

 the plastic clay, the Ashburnham beds, the corn- 

 brash, the inferior oolite, &c. ; and Mr. Lea gives 

 twenty-one as the number of fossil species of Unio 

 and one (doubtful) of Anodon. With respect to the 

 Unio Listeri, U. Hybridus, and U. concinnus, figured 

 in • Mineral Conchology,' Mr. Sowerby remarks that 

 these occurring in the oolite, together with U. cras- 

 siusculus, all want the distinguishing marks of the 

 genus ; and that judging by their hinges alone he 

 should hesitate to regard them as belonging to the 

 genus Unio. 



M. de Blainville, who divides the Na'idte (or his 

 Submytilacea) into two sections, viz. those which 

 have an epidermis, are nacreous, and the inhabitants 

 of fresh wafers ; and those which have no evident 

 epidermis, are not nacreo.is, and are more or 



less pectinated, places in the latter section the 

 genus Cardita and Subgenus Venericardia. This 

 genus is also approximated by Cuvier to the Unios ; 

 and M. Deshayes, commenting upon the position 

 assigned it by Lamarck, between Cardium and 

 Cypricardia (Fam. Cardiidce), observes that such is 

 not its true position, and we must here follow the 

 examples of Cuvier and De Blainville. The animal 

 resemoles that of Unio. The shell is very thick, 

 solid, equivalve, often very inequilateral, with the 

 umbones curved forwards : the hinge presents two 

 oblique unequal teeth ; one short and cardinal, the 

 other long, lamellar, bent, and placed much more 

 backwards. The ligament is elongated, subextemal, 

 and sunk into the shell. The muscular impressions 

 are rather large and distinct; the pallial impression 

 narrow. 



These mollusks are marine, and are generally 

 found on muddy or sandy bottoms, varying in dej)th 

 to forty or fifty fathoms. 



2939. — The Calt'cdlate Cabdita 

 (Cardita calycvlala). Nearly without exception 

 the Carditse have longitudinal ribs, the shell is solid 

 and heavy, and the lunule much sunk. In the 

 present species the shell is oblong, white, varied 

 with lunate spots of brown; the ribs are squa- 

 mous, the scales being arched, and incumbent; a 

 shows the shell with the umbones and lunule turned 

 towards the spectator. 



2940. — The Imbricate Cabdita 

 (Cardita ivihricata'). Venericardia imbricata. This 

 species of the genus or rather subgenus Vene- 

 ricardia occurs only in a fossil state ; the left-hand 

 specimen is from Grignon, that on the right is a va- 

 riety from Couitagnon. 



In uniting the species of Cardia and Venericardia, 

 says M. Deshayes, and placing them in their most 

 natural positions, the passage between them, as we 

 ])uisue the series, will be found to be so insensible 

 that it will be impossible to say where one com- 

 mences and the other terminates, and when the 

 internal characters are examined the same resem- 

 blance is observable as in the external forms. 



With respect to the number of species, M. 

 Deshayes in his tables makes out a list of twenty- 

 five, joining the two genera together; and of these 

 six are found both in a living and a fossil state. 

 In the last edition of Lamarck he gives the number 

 of living CarditfB as twenty-one, and observes that 

 of Venericardia the only living species noticed is 

 the V. Austialis, from the seas of New Holland. 



In the ' Proceeds. Zool. Soc' for 1832, three new- 

 species of Cardita are described by Mr. Broderip 

 (pp. 55, 56), and six species by Mr. G. B. Sowerby 

 (pp. 194, 195), all brought by Mr. Cuming from the 

 coasts of central America, the Gallapagos, and 

 some Islands in the South Pacific (Crescent and 

 Rapa Islands). 



One of these species, Cardita Cuvieri, far exceeds, 

 says Mr. Broderip, " in size and beauty any Cardita 

 hitherto discovered ; it was dredged from sandy 

 mud in eleven fathoms of water, about seven miles 

 from the shore (in Fonseca Bay). After its cap- 

 ture the dredge was kej)! at work for some hours, 

 but no other specimen could be procured. The 

 ribs are broad, flattened on their superior surface, 

 but very elevated and strongly geniculated ; the 

 geniculations being for the most part three-tenths 

 of an inch from each other. The shell is a very 

 striking object, and has the appearance of a carved 

 work." 



The number of fossil species of Venericardia and 

 Cardita are enumerated by M. Deshayes in his 

 Tables at fifty. In his last edition of Lamarck, the 

 number of Ibssil Venericardiie is given as ten, and of 

 CarditiB (fossil only) seven. 



Mr. Lea describes and figures four new species 

 from the tertiary of Alabama. (' Contributions to 

 Geology.') Dr. Mantell, Professor Phillips, Mr. 

 Lonsdale, Professor Sedgwick, Mr. Murchison, and 

 Dr. Fitton enumerate various species of fossil Car- 

 dita and Venericardia from the blue clay, the arena- 

 ceous limestone of Bangor ; the upper green-sand, 

 the Bath oolite, the inferior oolite, the Gosau de- 

 posit, and its equivalents in the Alps, the gault, &c. 



We may here appiopriately turn to another family, 

 the Polydonta of M. de Blainville, the Arcada of 

 I.amarck, placed by most writers near the Naidae, 

 and by M. de Blainville between these and the 

 Mytilidae. Lamarck places them between the NaYdee 

 and Cardiidse. 



Family ARCADE (Ark-shells, Area, Cucullasa, 

 Pectunculus, &c.). 



M. Rang characterizes the Arcadae as follows : — 

 The mollusk has the mantle entirely open through- 

 out its circumference, excepting towards the back, 

 without siphons or any particular apertures; and 

 partially adherent, sometimes prolonged backwards. 

 The foot is always very considerable. 

 The shell is generally thick, regular, equivalve. 



inequilateral, with a similar hinge in each valve, 

 always formed of a series of teeth, which are often 

 lamellar, fitting into each other, straight or oblique. 

 The muscular impressions are nearly always united 

 together by an intervening pallial mark, which 

 is narrow and runs parallel to the border of the 

 shell. 



The first genus, CucuUoia, is very limited in spe- 

 cies; only one, we believe, being as yet known. 

 The shell is thick, the umbones boldly elevated and 

 distant; the hinge is linear and straight; ligament 

 external ; teeth transverse and small, others oblique 

 and longitudinal ; anterior muscular impression 

 forming a projection with an angular border. The 

 general shape and appearance of the shell, which is 

 of moderate size, will be easily appreciated by re- 

 ference to the specimen. 



2941. — The Eared Ciicuu.jea 



(CucuUaa auricullfera). This handsome shell is a 

 native of the Indian Ocean, and occurs on beds of 

 sand. Externally the valves present both longitudi- 

 nal and transverse striae. The general colour of the 

 outer surface is deep cinnamon brown ; the internal 

 surface assumes a brown tinge towards the anterior 

 part, passing into violet. 



We now pass to the genus Area. The shell is 

 boat-shaped, rather thick, equivalve, but inequila- 

 teral ; the form is elongated, more or less oblique; 

 the umbones are distant, olten a little curved for- 

 wards, hinge linear and straight, with numerous 

 small interlocking teeth ; ligament external. M. 

 Rang remarks that the species sometimes adhere by 

 their foot, and more frequently by means of a 

 byssus. 



2942, 2943.— Noah's Ark 

 (Area Norn). Byssaarca Noae, Swainson. This 

 species, constituting the type of the subgenus Bys- 

 saarca, is a native of the Atlantic Ocean, and of 

 the seas of Europe. Mr. Swainson, who established 

 the subgenus, says, " The animals of these shells affix 

 themselves to other bodies, by a particular muscle ; 

 which is protruded through the gaping part of the 

 valves, rhey also adhere when young by means of 

 the byssiform epidermis, which covers the exterior. 

 A specimen now before us, which we procured in 

 the Bay of Naples, perfectly exemplifies this singular 

 property." 



In the 'Proceeds. Zool. Soc' 1833, p. 17 et seq., 

 will be found the description of fourteen new spe- 

 cies, by Mr. G. B. Sowerby. They were procured 

 by Mr. Cuming on the western coast of South Ame- 

 rica, and among the islands of the South Pacific 

 Ocean ; and were found moored to stones, shells, 

 and coral rock, at depths varying from the surface 

 at low water, to the depth of many fathoms. 



Referring to Fig. 2942, a shows the shell with the 

 valves closed, and the hinge towards the spectator ; 

 6, the valves closed, with the edge or inferior aspect 

 to the spectator, showing the hiatus; c, internal 

 view of one of the valves. 



At Fig. 2943, A is a lateral view of the shell with 

 the valves closed ; B, the shell with the hinge and 

 umbones presented ; C, a single valve showing the 

 hinge, a, the umbones ; b, the margin where the 

 valves gape to give room for the extrusion of the 

 tendinous foot. 



2944. — TuK ToKToocs Ark 



(Area tortuosa). Trisis tortuosa, Oken. In this 

 subgenus Trisis, the shell is twisted; the valves are 

 obliquely carinated ; the umbones small and 

 recurved. 



This species is a native of the Indian Ocean. 



Referring to Fig. 2U44, a represents the internal 

 view of one of the valves, showing the character of 

 the hinge ; b, the shell with the valves close, pre- 

 senting the inferior margin; c, the external view of 

 one of the valves. 



2945. — The Antique Abk 



(Area antiquata). The shell of this species is 

 transverse, obliquely cordate, ventricose, and many- 

 ribbed ; the ribs are transversely striated ; the pos- 

 terior ribs bifid. Colour white. The area auti- 



( quata is found in the Indian Ocean, on the coast of 

 Africa, and according to Lamarck in the Mediter- 

 ranean. According to M. Deshayes it has been 

 confounded since the time of Linnasus with another 

 species, both being included under the same specific 

 title ; yet he says that they are easily distinguished. 

 The true Area antiquata, figured in ' Gualt. 'lest. 'pi. 

 87, f. C. ; in 'Chemn. Conch.' t, vii., pi. 55, f. 5-18, 

 has the shell thicker, the ribs flatter and wider than 

 in the other species ; they are also striated, and there 



i are no furrows on the cardinal surface. The other 

 species is less solid, and more transverse, and has 

 the cardinal surface always furrowed when the valves 

 are united. He further remarks that the shell 

 figured by Poll and cited by Lamarck is a species 

 again distinct from these two. It inhabits the Me- 

 diterranean, and is the living representative of a 



