104 CRETACEOUS PELECYPODA 



The recent species of the TELLINACEA of which Tryon lately published a 

 catalo2;ue in pt. 5 of vol. iv, Am. Journ. Conch., 1808, are to hy far the greatest 

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

 bm-row in coi-als, 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 palaeozoic times ; they are scarce in the lower and not common in the 

 npper mesozoic epoch ; in the cainozoic epoch, liowever, their number increases 

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



A. TELLINA CEA with a cartilage in tlie hinge. 



IX. F,tmih/,—FAFIIIID.E. 



[MicsooESMiD.-r, (ilim Gray, Desh., Saiidljcrg-er, Ploernes, &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 sij^hons is considerably larger tban 

 in true Tellinidm. 



Shell solid, sub-trigonal, 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 whicb 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. Tlie 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- 

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



The family was first instituted by Dr. Gray under the name Mesodesmidj;, 

 but was subsequently by the same autlior replaced by that of PAPniiD.n (or 

 Papeiadjb). I consider tliis substitution as one thorougbly in accordance Avith 

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

 account of the subsequent introduction of the name Ilesodesma into concbological 

 literature.* 



* Mr. Deshayes states that Lamarck ilesi'rila-d two Jitferent generic forms \iniler the name of Paphia, and that 

 Lamarck h:id liinisclf given up the latter name. One of the two species is a Cnissdtelhi. proposed on thepreWons paj;e 

 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 Cra^sateUa must be struck 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 h.ad. 



