Naid«.] 



MUSEUxM OF ANIMATED NATURE. 



267 



believe, take any dye. Cuvier says, " Le Byssus 

 s'emploie pour I'abriquer des ctoiies prficieuses ;" 

 but this cannot, we imagine, be to any extent. All 

 we have seen of this fabric are merely gloves, 

 stockings, and the like. Small pearls are often 

 found on opening the shells. 



Fig. 2915 represents a, the young of the Pinna 

 flabellum beset with recurved spines : b, the inside 

 of one of the valves of a full-grown shell, one-fifth 

 natural size. 



Fig. 2916 represents a specimen of the Pinna 

 full-grown, with the byssus ; one-fifth natural size. 



With respect to the fossil Mytilidac, they are 

 not very numerous ; some however occur in beds 

 below the chalk, as well as in those above, but 

 especially in the crag. Of Mytilus, from ten to 

 fifteen appear to be determined. Of Dreissina, a 

 species occurs in the modern Calcaire in some 

 parts of Germany, and to this genus may be re- 

 ferred the Mytilus Brardi, Fig. 2917: — a, hinge and 

 septum enlarged ; b, outside of valve ; c, the inside 

 of ditto. 



Of Modiola, M. Deshayes, in his last edition of 

 Lamarck, enumerates twenty ; but to this number 

 a few other species have to be added. Of Litho- 

 domus five or six species appear to be known. With 

 respect to Pinna, several fossil species occur in the 

 secondary and tertiary beds of marine origin. 



Family NAIDvE (Fresh-water Mussels, Unio, 

 Anodon, &c. ; Les Anodontes and les Muletes of 

 Cuvier.) 



This interesting family is extensively spread ; the 

 rivers, fresh-water lakes, and pools of Europe produce 

 many species, but it is in the rivers of North 

 America that the group is most numerous. Dr. 

 L'?ach, Mr. Sivainson, Dr. Kirtland (in ' American 

 Journal of Science and Arts,' vol. xxvi.), and Mr. 

 Lea have greatly contributed to the elucidation of 

 this family. 



The genera are all closely related to each other, 

 the distinguishing characteristics being all of a 

 minor importance, insomuch that several genera 

 established by various naturalists have insufficient 

 foundations. Such at least is the opinion of Mr. 

 Swainson. 



Till very recently the Na'idne were regarded as 

 bisexual, like the oyster, edible mussel, &c., and 

 such was formerly Mr. Lea's opinion, as it had been 

 that of Lamarck, who obsei-ved the viviparous na- 

 ture of these mollusks, stating that the eggs pass 

 into the duct placed along the superior branchiae, 

 where the young are found with their shells com- 

 plete. In confirmation of this viviparous mode of 

 reproduction, Mr. Lea, as he states, on the dissection 

 of a specimen of Anodonta undulata (Anodon 

 undulatus), nearly three inches long, found the 

 egg-ducts charged with about six hundred thousand 

 young shells perfectly formed, both valves being 

 distinctly visible with the microscope. 



While pursuing his observations on these fluviatile 

 mollusks. Dr. Kirtland, of Poland, Ohio, informed Mr. 

 Lea of the fact that these mollusks were indivi- 

 dually males, and individually females ; and that he 

 was able to distinguish between the malesand females 

 by the form of the shell, without having recourse 

 to the included animal. Shortly afterwards, Dr. 

 Kirtland's paper on the subject appeared in the 

 'American Journal of Science and Arts.' 



Mr. Lea then instituted a series of observations 

 which fully satisfied him as to the truth of the in- 

 dividual difference of sexes. The female sustaining 

 her very large burden, naturally requires more 

 space within the valves : hence, as compared with 

 tnat of the male, the shell at its posterior part is 

 generally enlarged, difTeiing however in form in 

 the various species. This difference of form, easily 

 seized on by a practised eye, is the distinguishing 

 criterion by which the females are to be recog- 

 nized. 



The observations of Mr. Lea are accompanied by 

 explanatory illustrations, of whicb we here avail 

 ourselves. 



Fig. 2918 and 2919 represent the Unio irroratus. 

 At Fig. 2918 the shell is seen in an internal and 

 external aspect; at Fig. 2919, A represents the 

 soft parts, showing the interior of the oviduct ; B, 

 the exterior of the same, a, the mouth ; b, the 

 great adductor muscle ; c, the right superior bran- 

 chia; d, the great posterior muscle; e, the infe- 

 rior right branchia ; f, the right oviduct ; g, the 

 foot ; /(, the superior left branchia ; j, interior view 

 of oviduct. 



At Fig. 232(1, Unio ochraceus, and at Fig. 2921, 

 Unio cariosus, the appearances exhibited by the 

 female molUisk are displayed, one of the valves 

 being removed and the oviducts exposed. These 

 sacculated repositories would almost induce us to 

 term the animals marsupial mollusks. In these the 

 eggs, subjected to the action of the water, become 

 developed, the young, previously to exclusion, being 

 rovcrcd by their shells, and, except in size, differing 

 little from their parent. 

 Vol. II. 



Fig. 2922 represents the female of Anodonta 

 fluviatilis (.Anodon fluviatilis). In his paper on the 

 Lamellibranchiate Conchifera, Mr. Garner gives a 

 figure of the young animal from the eggsac of an 

 Anodon, as seen in the field of a microscope, one- 

 third of an inch focus. 



Fig. 2923 represents the mollusk of Anodonta 

 undulata (Anodon undulatus). 



Mr. Lea remarks that the mass of lobes in this 

 species differs from the mass of lobes in A. fluvi- 

 aiilis, the tint being darker, and the arrangement 

 of the oviducts very remarkable. The ova or eggs 

 are placed in a kind of sac, lying across the lobe, 

 and presenting one end to the stomach, the other 

 to the mantle of the animal. They lie so closely 

 together as to assume on the exterior a form like 

 that presented by the cells of a honeycomb. This, 

 says Mr. Lea, is of course produced by pressure. 

 Some of these sacculi when carefully opened were 

 found to contain as many as twelve ova; each with 

 a perfect living shell in it, having a brown epi- 

 dermis. Referring to Fig. 2023, o, represents a sac- 

 culus with its ova: b, the egg or ovum with its 

 perfect young shell included; c, the honeycomb 

 appearance, the portion being eight times mag- 

 nified. 

 ; Figs 2924 and 2925 represent two females of Unio 

 radiatus, as they lay at rest on the bottom of a basin 

 of water : Mr. Lea observes that these females exhi- 

 bited two very different forms as regards the inferior 

 portion of the mantle. These differences will be 

 seen by reference to the figures. 



With respect to the food of the Naidae it appears 

 to consist of minute animal and vegetable matters, 

 ^Mr. Lea says that he has strong reasons for be- 

 lieving that the former constitute their principal 

 support. Animalcules indeed abound in all current 

 or stagnant water, and these he thinks the mollusks 

 separate, from the constant stream which leaves the 

 branchisB and passes out by one of the siphons. The 

 operation he witnessed frequently in a vessel in 

 which he kept the Naidae for some months. If 

 the water was not changed for twenty-four hours, 

 he uniformly found the animals quiet, but within 

 a few minutes after it was changed, they as uni- 

 formly commenced the passage of this con-^tant 

 stream. He adds that he cannot suppose this opera- 

 tion to be for the sole purpose of breathing, as there 

 is no intermission in the stream of water, and the 

 quantity thrown out is too great for this purpose 

 I only. He therefore believes it to be the result of 

 the action of the separation of the animalcules from 

 the water. Of this however there is no definite 

 proof, and we must remember the stimulus which 

 the internal organs and branchiae would receive 

 from the fresh water, and though this rapid trans- 

 mission of fluid may subserve the purpose of ac- 

 quiring food, yet we suspect that the action in 

 question resulted from the change of spoiled and 

 exhausted water, for that replete with oxygen. 



The shells of the Naidae are many of them lined 

 with a most brilliant nacre, and are besides of con- 

 siderable thickness. Wiien we consider the origin 

 of pearls and their identity with nacre, it will not 

 surprise us to learn that these valued ornaments are 

 abundantly produced by many species. One species 

 indeed, abundant in our rivers, namely the Mya 

 margaritifera of Linnaeus (Unio elongatus), has 

 been long celebrated for this production, and 

 according to Pennant there were formerly regular 

 pearl-fisheries established on many of our rivers. 

 As early indeed as the time of the invasion of our 

 island by Julius Cirsar, British pearls were cele- 

 brated ; and, according to Suetonius, one induce- 

 ment at least to the descent of the great Roman 

 and his legions on our island was the acquisition 

 of these valuables — not that we credit such a story ; 

 statesmen and warriors are influenced by far 

 diiferent motives in their plans of usurpation and 

 conquest. It would however appear that Caesar 

 dedicated a brea.st-plate adorned with British pearls 

 to Venus, in her temple ; but Pliny, who speaks 

 of the pearls of our island, refers to these very 

 specimens (which were small and ill-coloured) as 

 a proof of their inferiority. 



In far later days, however, several rivers were 

 noted, — among these were the Esk and the Conway. 

 In the days of Camden (who died in 1623), the 

 latter river had not lost its reputation ; and Sir 

 Richard Wynn of Gwydir, chamberlain to Catherine, 

 queen to Charles II., is said to have presented her 

 majesty with a Conway pearl, which, says Pennant, 

 h to this day honoured with a place in the regal 

 crown. The river Irt in Cumberland was also 

 famous for pearls, and the circumnavigator Sir 

 John Hawkins had a patent for the pearl-iishery of 

 that river. 

 j Nor is it fo the rivers of England alone that 

 I pearl-bearing mussels are limited. Ireland is not 

 I without her share, and some specimens of consider- 

 able size and value have been procured, especially in 

 the rivers of Tyrone and Donegal ; we are informed of 

 one which weighed thiity-si-c carats (a ca: at is neirly 



four grains), and was estimated at forty pounds, but 

 was not of perfect shape and colour, otherwise it 

 would have been more valuable. Other pearls have 

 been sold /rom four to ten pounds, and one purchased 

 at the latter sum was deemed so admirable, that, as 

 Pennant states, Lady Glenlealy refused eiglify 

 pounds for it from the Duchess of Orniond. 



We have seen pearls from the Unio of our rivers, 

 but none of any size or great clearnes.s. 



With respect to locomotion, — as they want the 

 byssus, these mollusks are never attached, and the 

 large foot serves them as a sort of propeller in 

 traversing the muddy floor of the pond or river : 

 in order to execute these movements, they paitially 

 open the valves, protrude the foot, and gradually 

 set themselves up on their edge ; they then proceed 

 by a series of impulsive movements, leaving a fur- 

 row in the mud behind them. 



The genus Unio is distinguished by cardinal 

 teeth; the right valve has anteriQrIy a short fosset, 

 for the reception of a tooth of the left valve, and 

 behind this a thin lamina or ridge, received into 

 a furrow between two laminae of the left valve. 

 In the genus Anodon there are no cardinal teeth. 



Mr. Lea arranges the Naidae in two groups, 

 which he terms Margarita (a title preoccupied) and 

 Platiris. 



Group MARGARITA. 



Subgenus Unio. — Having a cardinal and lateral 

 tooth. 

 Symphynote. — Example, Unio alatus. 



2926.— Thk Winged Unio 



( Unio alatits). a, part of the wing of the valve 

 broken off, showing the symphynote character re- 

 duced. 

 Non-symphynote. — Example, Unio pictorura. 



2927. — The Paimters' Mussel 



{Unio pictoium). This well-known species, of 

 which our figures represent the young shells, is 

 very common in our rivers. Several specimens 

 from the Thames are now before us. The valves 

 are of tolerable thickness. 



Subgenus Margaritana, — Having one tooth, 

 cardinal. 



Non-symphynote. — Example, Alasmodonta undu- 

 lata, Say. 



2928. — The Undulated Unio 



(^Alasmodonta undulata, Say). This species is a 

 native of North America. 



Symphynote. — Example, Alasmodonta compla- 

 nata. 



2929. — The Flattened Unio 



(Alasmodonta complanata). This species is re- 

 markable for its flattened form, and wing-like 

 appendage, resembling that of Unio alatus. 



Subgenus Dipsas. — Having a linear tooth on the 

 dorsal margin. 



Symphynote. — Example, Dipsas plicatus. Leach 



2930.— The Folded Unio 



(Dipsas plicatus). The term Dipsas is inadmis- 

 sible, time immemorial it has been appropriated 

 to a species of serpent. 



Subgenus Anodonta (Anodon). — Having no 

 teeth. 



Symphynote. — Example, Symphynota magnifica. 

 Lea. 



2G-31. — Thk Sple.-vdid Anodon 

 {Symphynota magnifica. Lea). Anodon magni- 

 ficus. 



This beautiful species was first described by Mr.. 

 Lea ; it is a native of North America. 



Non-symphynote. — Example, Anodon fluviatilis. 



2932. — ^The Fluviatile Anodon 

 {Anodon fliii'iat His). This species is common in our 

 fresh waters. 



Group PLATIRIS, Lea. Non-symphynote. 



Subgenus Iridina. — Having a crenulate dorsal 

 margin. Example, Iridina exotica. 



2933. — The Exotic Iridina 



(Iridina exotica). Lamarck gives the rivers of 

 warm climates as the locality of this genus. The 

 present species (Iridina elongata, Sowerby) is sup- 

 posed to come from China. M. Caillaud found it 

 (if the species be identical) in the Nile, in con- 

 siderable abundance, but we suspect that M. 

 Caillaud's specimens are referable to a species 

 described and figured in the 'Zool. Journal,' vol. 

 i., by Mr. G. B. Sowerby, under the name of 

 Iridina nilotica, obtained in Sennaar by M. Cail- 

 laud, and sent to England by M. DAude- 

 bard. Its hinge margin is not crenulated or den- 

 tated. Mr. Lea makes it the type of a distinct 

 subgenus. 

 Subgenus Spatlia.— Dorsal margin non-crenulate. 



2M2 



