104 CEETACEOUS PELECYPODA 



Tlie recent species of the TELLINACEA of wliicli Try on lately published a 

 catalogue in pt. 5 of vol. iv, Am. Journ. Conch., 1868, are to by far the greatest 

 extent inhabitants of moderate depths of the sea and of sandy shores ; only very few 

 burrow in corals, in which cases some modifications in the form of the foot are to 

 be observed. With respect to geological age we have no sufficient proof of their 

 existence in palgeozoic times ; they are scarce in the lower and not common in the 

 upper mesozoic epoch; in the cainozoic epoch, however, their number increases 

 considerably, but hardly equals half of what it is at the present time. 



A. TEL LIN A CEA with a cartilage in the hinge. 



IX. Famlh/.—F AFHIIDyE, 

 [Mesodesmjd^:, olim aT'Ay,J)e^h,, Sandberger, Hoernes, &c.). 



The animals, as far as they have been examined, are typical TELLINACEA, 

 inasmuch as the siphons, though short and thick, are separated from their bases, 

 the foot is lingui-form, laterally compressed ; the palpi are, however, rather short and 

 the two gills on each side unequal ; the mantle is widely open only in front and 

 narrowly behind ; the united portion below the siphons is considerably larger than 

 in true Tellinid^e. 



Shell solid, sub4rigonal, or transversally oblong, closed all round, equivalve, 

 generally inequilateral, the posterior side being often the shorter one ; hinge with an 

 internal cartilage-pit and usually with one cardinal tooth on each side of it ; lateral 

 teeth variable, present either on both sides or only on one, or entirely obsolete ; ligament 

 externally above the cartilage-pit either distinct, though always very thin, or only 

 indicated by a thickening of the epidermis which covers the shell ; muscular impres- 

 sions strong ; pallial line generally with a small posterior sinus, occasionally entire. 



It is more the combination of certain characters which distinguish this family, 

 than their peculiarities as regards other allied forms. The animals a great deal 

 resemble those of Donax, and the shell is in external shape equally often very 

 similar in both, while the presence of a cartilage places them next to the Scrobi- 

 culahubm, from which, however, the animal and shells greatly differ. 



The family was first instituted by Dr. Gray under the name 3Ie8odi:8mib.e, 

 but was subsequently by the sanje author replaced by that of Faphiijdm (or 

 Papeiadm). I consider this substitution as one thoroughly in accordance with 

 the laws of priority, and by no means undesirable (as Deshayes says) on 

 account of the subsequent introduction of the name Mesodesma into conchological 

 literature.* 



«= Mr. Deshayes states that Lamarck described two dlflferent generic forms under the name of Paphia, and that 

 Lamarck had himself given up the latter name. One of the two species is a Crassatella, proposed on the previous page 

 of the same work, to which genus, Deshayes admits, the species must be referred ; for the other, the name Paphia 

 must, in my opinion, be retained, but not replaced by a new one, as suggested by Deshayes ; for if that plan was to 

 be adopted, it would necessarily follow that the name Crassatella must be strack off the list also, as there equally was 

 a mixture of species in it similar to that of the present genus. Lamarck had, as I have already pointed out, no 

 more right to change or abandon any of his names introduced into science, than any one else had. 



