OF SOUTHEEN INDIA. 95 



ranniug iiosteriorly ; anterior muscular impression very elongated, runnino- from 

 tlie beaks posteriorly in an oblique direction, pallial line anteriorly truncate. 

 The forms of Ensis are not as yet known from mcsozoic formations. 



3. Sol(;nopsis, M'Coy, 1841, (Carb. Foss. of Ireland, ed. 18G2, p. 47). Shell 

 like Solen, but somewhat thicker anteriorly and with inflated beaks ; posterior end 

 truncate. This genus has been proposed for the reception of some palaeozoic species, 

 formerly described as Solen, like S. pelagicus and vetudns of Goldf uss, S. siUqiioides, 

 Kon., and others. The general form of these shells is very much like that of 

 elongated species of Splieiiia ; the hinge-teeth, if any, are not as yet known, and 

 it is therefore, strictly speaking, impossible to classify the genus correctly ; 

 d'Orbigny identifies it with Lijonsia. 



4. Solenarki, Stoliczka, 1870. Shell thin, narrow, long and straight, like a 

 Solen, internally with two radiating diverging ribs, originating at the beaks and 

 proceeding towards the ventral edge. I propose this genus for Legnminaria offinis, 

 Eichwald (Leth. Eoss., XI, 1867, p. 788, pi. xxvi, fig. 12,) from the Turonien 

 beds of Eussia. The hinge is as yet not known, but the general form of the shell 

 entirely agrees with Solen. 



5. CuUellus, Schuhmacher, 1817. Shell compressed, ovate, slightly curved, 

 gaping at both ends ; anterior muscular impression rounded, posterior ano-ulai-, 

 pallial sinus small; hinge, according to Deshayes (Paris Fossils, II edit., 1864, 

 p. 155,) with two teeth in the right, and one or two in the left valve. Schuhmacher 

 and subsequent authors indicate three teeth in the right valve, but Deshayes says 

 that he never found more than tAvo. Possibly one is very small and occasionally 

 obsolete, but if it actually ever exists the genus stands very close to Misis, differ- 

 ing from it by the form of the anterior adductor muscle, the greater height of the 

 shell in proportion to its length and the short rib below the beaics. There are ncj 

 species known to occur in rocks older than the eocene with reliable certainty. 



5a. Ensiculiis, H. and A. Adams, 1860, (Proc. Zool. Soc, p. 369), has been 

 proposed for the old Solen Cultellits, Lin., differing from the other species of 

 CuUellus by its more elongated, curved, and parallel form, and the short oblique 

 ribs below the umbones. 



6. Slliqua, Miihlfeld, 1811. Shell compressed, straight, or slightly curved, 

 thin, covered with a polished epidermis ; beaks supported by an oblique strouf 

 rib, right valve with two, left with three teeth in the hinge ; in the former they are 

 usually distant, and occasionally there appears a third one between both; pallial 

 sinus broad and deep. 



Types of shells very similar to the recent SlUquce already occur in paleozoic 

 rocks, but as their hinge-teeth and pallial sinus are not known, it is impossible to 

 distinguish them from Solemycu. Somewhat better characterized are the forms of 

 Slliqua in Jurassic and cretaceous deposits, and their number gradually increases un 

 to the present date. 



