BItACIlIOPODA. 
41 
Par. y.-SUBDIVISA- 
Plate 4, figs. 11, 12. 
Var. y .—Planior ? 8-20 costata, costis triliclis, saepe quadrifidis, 
ard marginem vix regularibus. 
In this variety the division of the ribs is carried further than 
in the preceding one; the principal ribs, which are narrow 
and almost angular (not rounded, as in the type variety) being 
divided into four or five coarse striae; the central one scarcely 
preserves a greater prominence than the rest. 
The median furrow in the convex dorsal valve is better pre¬ 
served in this shell than in Var. j3. The hinge line is of full 
length, the ventral valve flat or slightly concave, and the size 
the same as in other varieties. 
Locality. —Kalajowar; 15,800 feet (1705, 1766), Chorhoti 
Pass (1737, 1752), &c., &c. 
Var. — STRIATO-COSTATA. 
Plate 4, figs. 13, 14. 
Var. t ).—Convexior bilobata, costis circiter 24, fere per totum 
bi- vel tri- fidis. 
This variety completes the series for this variable shell; the 
central furrow is deeper,—the ribs themselves have become 
more numerous, and not having room for regular trifurcation, 
they divide into two, three, or four, according to the space, the 
intermediate ribs starting almost from the beak. 
The general character of the shell is preserved even in this 
extreme variety, which resembles in this respect, as it does also 
in form, the English fossil 0. fiabellulum, Sow. In both 
species the type variety has simple rounded ribs, and from this 
form a series of variations leads us to a shell which would 
almost be called striate, if its real affinity with the coarse- 
ribbed shell above described were not easily traceable. 
Locality. —Rimkin. Marked (R) in the collection. 
G 
