MOLLUSCA. 
25 
occurs, opposite to tlie sinus on tlie ventral margin. This is 
a character common to several species. 
Locality .—Foot of the Niti Pass, 1(3,000 feet. (No. 1780.) 
CTENODONTA.-Sp. 
Plate 2, fig. 21. 
About half an inch wide, and one quarter high, convex, 
ridged diagonally, and pointed behind. The form is subovate 
acute, the beak prominent, and the diagonal bluntish ridge 
contributes to give a triangular look to the entire shell, 
though it is really subovate. Surface . . . . ? It is 
too imperfect to name, but is like many another Silurian 
species. 
Locality .—Same as last. (No. 1780.) 
CYRTODONTA ? IMBRICATULA. 
Plate 2, fig. 22. 
Transversa, oblonga, a nate omnino laterali usque ad marginem 
posticum tumida (auriculo minori postico piano) inde per marginem 
ventralem latusque anticum brevissimum rotundum plana. Striaa 
concentricse confcrtac filosrn. 
Transverse-oblong, tumid along the posterior slope, and 
flattened elsewhere, with a lateral almost overhanging beak, 
which, however, is not prominent. The hinge line straight, 
and with a small square flat ear posteriorly. The surface is 
concentrically striated, or rather fine-ribbed. The strise are 
prominent (thread-like on the posterior ear), and tolerably 
regular in position throughout, though they appear fasciculate 
in places. 
The anterior side beneath the beak is remarkably flattened, 
and this is not due, I believe, to pressure. The hinge cannot 
be seen, and hence the genus (described by Billings) is rather 
uncertain. 
Locality .—Foot of Niti Pass, as before. (No. 1780.) 
VOL. II, 
E 
