OF SOUTHEEN IXDIA. 293 



cancelled, and the species referred to Cypinna, with which the shell perfectly a"-rees 

 in form. It was first descrihed as F<?«?<^«7es, under which name Schlotheim made 

 known a large number of fossil shells, extei-nally resembling Venus (in the old 

 sense of the term and rather applyiug to Cytherea, as restricted). 



2. Fti/chomi/a, Ag., 18-12, (vide Pictet and Camp., Pal. Suisse, i""" scr., p. 350). 

 Shell orately elongated, moderately compressed, beaks close together, placed sub- 

 anteriorly, surface radiately ribbed, anteriorly generally divaricately striated ; 

 hinge with three diverging cardinal teetli in each valve, tlie posterior ones very 

 elongated, double in the right valve, and the cartilage pit situated in front of them ; 

 muscular impressions elongately oval, rather large; pallial line truncate poste- 

 riorly. Type, Ft. plana, Ag., fCrassatella Robinaldina, d'Orb.). 



Pictet and Campiche have pointed out the distinctions of this genus from 

 Crassatella ; they chiefly note the external differences in the ornamentation of the 

 shells, but there is also a considerable difference in the arrann-emeut of the hino"e- 

 teeth. The species of Ftychomya as yet known are few, and most of thom appear to 

 belong to the cretaceous period. Lycett named an oolitic shell. Ft. A(jas.sizl, whicli 

 I noticed under Myocliama (p. 61). 



Fadioconclia, Con., 1869, (Am. Journ. Conch., v, p. 17,) is noted as "Com- 

 pressed, inequilateral, radiated ; hinge without a distinct cardinal pit. C. Gueran- 

 geri, d'Orbiguy; C. Bohlnaldina, d'Orbigny." Such is the n^onderful charac- 

 teristic of one of Mr. Conrad's wonderful new genera! This almost amounts to 

 an abuse, setting aside the disregard or neglect of the work of previous authors. 

 The first species is a Crassatella, and has no radiating ribs ; the second is the 

 type of Agassiz' Ftijchomya. What should be thought of Mr. Conrad's other 

 genera of Ceassatellibm, if they are based upon similar principles ? 



3. Antlionya, Gabb, 1861, (Pal. Calif., i, p. 181). Shell narrow, compressed, 

 posteriorly very elongated, anteriorly shortly rounded, beaks obtusely pointed; 

 hinge with two elongated, somewhat diverging cardinal teeth in each valve ; a pit 

 is seen posterior to them in both valves, and judging from the general resemblance 

 of the shell to Crassatella, it is probably destined to receive a cartilage. Type, 

 A. cultriformis, Gabb, from cretaceous deposits of California. 



4. Crassatella, Lam., 1799. Shell elongately oval, compressed, or moderately 

 tumid, inequilateral, posteriorly generally somewhat prodnced, beaks close toge- 

 ther ; hinge with two anterior elongated cardinal teeth in each valve, the cartilage 

 pit posterior to them ; a posterior sub-lateral tooth parallel to the hinge maroiu in 

 the right valve, it fits into a corresponding marginal groove of the other valve, a 

 more or less distinct elongated tooth being situated below it ; the right valve usually 

 also has a minute anterior lateral tooth and the left a corresponding small pit ; 

 muscular impressions roundly oval, posterior, as usually, larger than the anterior, 

 and both are moderately excavated. 



There are two somewhat distinct forms included in this genus. All the 

 cretaceous and many eocene species have a rather high sub-triangular form, two 

 large strongly diverging cardinal teeth in the left valve, the posterior tooth 



