OP SOUTHEEN INDIA. 95 



running posteriorly; anterior muscular impression very elongated, running from 

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

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



3. Solenopsis, M'Coy, 18M, (Garb. Foss. of Ireland, ed. 1862, p. 47). Shell 

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

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

 formerly described as Solen, like S. pelagicus and vetustus of Goldfuss, S. siliquoides, 

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

 elongated species of Sphenia; 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 Lyonsia, 



4. Solenaria, 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 Leguminaria affinis, 

 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. CiiUellus, Schuhmacher, 1817. Shell compressed, ovate, slightly curved, 

 gaping at both ends ; anterior muscular impression rounded, posterior angular, 

 pallial sinus small; hinge, according to Deshayes (Paris Eossils, 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 two. Possibly one is very small and occasionally 

 obsolete, but if it actually ever exists the genus stands very close to JEnsis, difi'er- 

 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 beaks. There are no 

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



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

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

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

 ribs below the umbones. 



6. Siliqua, Miihlf eld, 1811. Shell compressed, straight, or slightly curved, 

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

 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 Siliquce already occur in palaeozoic 

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

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

 Siliqua in Jurassic and cretaceous deposits, and their number gradually increases up 

 to the present date. 



