1863. ] On Dr. Gerard’s collection of Spiti fossils. 129 
7. AMMONITES TENUISTRIATUS, Gray. 
A. tenuistriatus, Gray, Hardwicke’s illustrations. 
A single cast containing a portion of the body whorl in which is 
a beautiful cast of an Aptychus, is to be referred doubtfully to the 
above species. The curvature of the ribs is similar to that of the 
type, but the whorls are narrower and rather thicker. Judging from 
the few specimens I have seen, A. tenwistriatus appears, however, to 
be very variable in this respect, and I refer the Spiti specimen there- 
fore provisionlly to this species. 
8. AMMONITES BIPLEX, Sowerby, Plate II. fig. 5, Plate III. figs, 
4, 4a—e, 5. 
Ammonites. Everest. As. Res. Vol. XVIII. Pt. II. p. 114, Pl. 1. 
figs 2, 3. 
A. annulatus. Sowerby. Op. et. vol. cit. p. 278. 
Several specimens of an Ammonite, which I cannot distinguish 
from the well known Oolitic species above quoted, occur in the col- 
lection, in black siliceous nodules. One large specimen measures 5 
inches and 2 lines in diameter. Others less perfect, from 8 to 3% 
inches. The width of the outer whorl varies from ;33, to ;3% in the 
more typical specimens, and the aperture is almost orbicular, slightly 
flattened at the sides. The ribs are sharp and numerous, and bifur- 
eate very regularly at about 2 across the whorl. Most of them 
have an occasional deep suleation, indicating the position of a pre- 
vious mouth. The sutures correspond closely to that figured by M. 
D’Orbigny in the Pal. Franeaise. 
In addition to the above, two specimens, which at first I hesitated 
to regard as the same species, have the ribs much more numerous, 
and the whorls wider ; the outer whorl being 3.8, and ,4,', respective- 
ly, of the diameter. That with the latter measurement is moreover 
more compressed than the typical specimens, the thickness being 
15 only. On consideration, however, I can see no good reason for 
regarding these specimens as specifically distinct from the more typi- 
eal. Their sutures are very similar, and as regards form, the narrow- 
er whorled of the two differs but little from the type, while the 
peculiar close set ribbing distinctly indicates the specific identity of 
the two. One of these is figured at Plate IIT. figs. 4, 4a. 
An important point to be noticed in comparing full grown speci- 
