MOLLUSCA. 
Ammonites. 
244 
The Pleistocene Marine Formation, Ireland. 
13. Dentalium giganteum. —The Gigantic Dentalium, pi. 
XCVIIIL fig. 68. 
D. giganteum. Phillips, Geo. York. I. pi. 14, fig. 8. 
Considerably arcuated, smooth; with several strong furrows 
at the narrowed, apical end; a narrow line extending more 
than half the length from the base; surface smooth. 
The Lias, Robin Hood’s Bay, Yorkshire. 
14. Dentalium septangulare. —The Seven-angled Denta¬ 
lium, pi. XCVIII. fig. 58. 
D. septangulare. Edinburgh Phil. Journal, XII. pi. 9. 
Smooth, shining, gradually tapering to a pervious point, with 
seven strong, longitudinal, smooth, even ribs. 
The Greensand, Belfast. 
15. Dentalium strangulatum. —The Strangled Dentalium, 
pi. XCVIII. fig. 60. 
D. strangulatum . Deshayes, Monog. pi. 16, fig. 28. 
Cylindrical; scarcely tapering; smooth; a compressed, 
narrowed space near the base. 
The London Clay, Barton. 
APPENDIX. 
CLASS MOLLUSCA. 
1 . Ammonites Allasii. —Alias’s Ammonite, pi. XX.* fig. 1 . 
Six rounded volutions, which are wholly exposed, and crossed 
by numerous transverse, equidistant bent ribs. 
In the Lias, Yorkshire. 
2. Ammonites furcatus. —The Forked Ammonite, pi. XX.* 
fig. 2. 
A. furcatus. Sowerby, Geo. Tr. 2nd Ser. IV. p. 339, pi. 14, 
fig. 17. 
Discoidal, sides and front fiat; inner volutions partly visible; 
aperture with a square front, rather oblong, and deeply impressed 
by the preceding volution; lateral angles truncate; ribs rather 
distant, thick, curved, many of them forked, and passing at 
right angles over the front. 
The Lower Greensand, Hythe and Atherfield. 
3. Ammonites cristatus. —The Crested Ammonite, pi. XX.* 
A. cristatus. Sowerby, Geo. Tr. 2nd Ser. IV. p. 377, pi. 11, 
fig. 23. 
Moderately compressed, with a sharp smooth keel; transverse 
ribs very irregular, some being largely furcated, and bent, 
while some are single, and others only extend over half the 
volution. 
In the Gault, Folkestone. 
4. Ammonites crknatus. —The Crenated Ammonite, pi. 
XX.* figs. 5, 6. 
A. crenatus. Sowerby, Geo. Tr. 2nd Ser. IV. p. 337, pi. 
II, fig. 22. 
Sides flattened, inner volutions much exposed, with nearly 
smooth and rounded margins; those of the outer volutions 
crenated on each side, of a concave space over the siphuncle. 
In the Gault, Folkestone. 
5. Ammonites symmetricus. —The Symmetrical Ammonite, 
pi. XX.* figs. 17. 18. 
A. symmetricus. Sowerby, Geo. Tr. IV. p. 337, pi. 11, f. 21 . 
Aperture almost square; provided with a rounded and 
notched keel; ribs obtuse; a little tumid as they approach 
the hollow in which the keel is immersed, and very uniform in 
point of elevation ; sides of the volutions flattened. 
The Gault, Folkestone. 
6. Ammonites ctrcularis.— The Circular Ammonite, pi. 
XX.* figs. 9, 10. 
A. circularis. Sowerby, Geo. Tr. 2nd Ser. IV. p. 337, pi. 11 , 
fig. 20. 
Aperture circular; volutions just touching each other; nearly 
close, acute, and circular ; surface sometimes with transverse 
ridges. 
The Gault, Barham and Maidstone, and the Oxford Oolite, 
Abbotsford, Dorsetshire. 
7. Ammonites trisercalis.— The Three-Tubercled Ammon¬ 
ite, pi. XX.* figs. 20, 21. 
A trisercalis. Sowerby, Geo. Tr. 2nd Ser. IV. p. 344. 
Discoidal, with a flattened margin; umbilicate; sides with 
a series of straight transverse ribs, each provided with a rounded 
obtuse tubercle on its outer end; the marginal portion of the 
rays provided with three rows of tubercular protuberance, and 
about ten tubercles around the umbilicus ; aperture nearly 
square. 
The Greensand, Blackdown. 
8. Ammonites Cookii. —Cook's Ammonite, pi. XX.* fig. 7. 
Aperture oblong; volutions moderately inflated, rapidly 
increasing, the inner ones more than half concealed; surface 
smooth, with narrow I'ibs extending from one side to the other, 
every alternate one forked, and the intermediate ones only 
extending two-thirds across the volutions, from the ambit, 
which is slightly flattened with the ribs passing over it; four 
volutions. 
9. Ammonites Comptoni. —Compton's Ammonite, pi. XX.** 
fig. 7. 
A. Comptoni. Pratt, Ann. Nat. Hist. VIII. p. 163, pi. 4, f. 1. 
