OF SOUTHERN INDIA. 359 



be said rather to belong to the past thau to the in-esent epoch. Several of the 

 species of Finna, of Inoceramus, and of other Avicvlibm, belong to the most char- 

 acteristic fossils of various formations. 



XXXYII. Family— PEASINIB^. 



I have jilaced in this family a few genera the classification of which is some- 

 what arbitrary. They are Modiolopsis, IIlppo}nua, MyoGoncha, Uippopodinm, Fra- 

 sina, Julia, and Fhaseolicama. Most of the species are fossil forms, which in 

 general shape and character of shell exhibit, as already alluded, distinct relations 

 to the Mttilid^. Both have the same elongated, very inequilatei-al form, more 

 or less narrowed or even pointed at the beaks, and the muscular impressions are 

 in all also similarly placed, subject to slight variations. The character of the 

 external surface is also iu both families the same. The hinge-teeth which, however, 

 occur in some of the genera of the present family indicate a relation to those 

 of the Cardites, and for this reason Deshayes associated the fossil Myoconches 

 with the last named genus, which classification was adopted by some conchologists. 

 In such transitional forms as those included in the present family, single characters 

 should less than any others be considered as leading, and, for the above noted, more 

 general, reasons, I prefer to follow d'Orbigny's suggestions regarding the classifica- 

 tion of llyoconcha near Jlylilns. This view has, it appears, also lately been supported 

 by Deshayes, who admits the relation of the recent Frasina to the Mttihd^. 

 Now, Frasina, as well as Julia, are generically perhaps hardly separable from the 

 fossil Ilippopodium, and this again shows iu its hinge-character the greatest affinity 

 to Myoconcha. Fliaseolicama may be considered as the reprcsentant of the fossil 

 Modiolopsis, and it is possible that the recent Jlodiolarca, of which I spoke in the 

 Glossiv^ (see p. 181), may also be conveniently grouped in this place. 



The distinguishing characters of the shells consist in the elongated, very 

 inequilateral form of the valves, with moderately tumid beaks, more or less smooth 

 sm'face, two unequal muscular impressions, of which the anterior is smaller, but 

 more deeply excavated, the posterior large, shallow, and sometimes rather vcntrally 

 placed. A partial division of this muscular scar leads me to suppose that the 

 greater part of the impression is produced by the pedal muscle and not by the 

 posterior adductor, to which, as in the Mytilidm, very likely only the upper or 

 dorsal part of the impression is to be attributed. The hinge, as far as known, 

 appears to consist of one elongated cardinal tooth in each valve ; the ligament is 

 external, long, supported by thickened fulcra. Only in Modiolopsis and Fhaseoli- 

 cama no hinge-teeth have been observed. 



Of the two or three recent genera, Frasina, Julia, and Fhaseolicama, the 

 animal of only the last named one has been recorded. It appears to have the 

 mantle margins united, with one pedal and two siphonal openings. This clearly 

 indicates a passage to some of the Dreissenidje, as already pointed out. 



1. Ilodiolopsis, Hall, 1847, (Palajont., New York, I, 157). Shell elongated, 

 very inequilateral, with the beaks anterior, sub-terminal, and close together, thin, 



1 T 



