244 



MOLLUSCA. 



Ammonites. 



The Pleistocene Marine Formation, Ireland. 



13. Dentalium GiGANTEUM. — The Gigantic Dentalium, pi. 

 XCVIIII. 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 septangulaee. — 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. 00. 



D. strangulatum. Deshayes, Mouog. pi. 16, fig. 28. 



Cylindrical ; scarcely tapering ; smooth ; a compressed, 

 narrowed space near the base. 



The London Clay, Barton. 



APPENDIX 



CLASS MOLLUSCA. 



I. 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. 



i2. 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 flat ; 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 ceenatus. — The Crenated Ammonite, pi. 

 XX.* figs. 5, 0. 



A. crenatus. Sowerby, Geo. Tr. 2nd Ser. IV. p. 337, pi. 

 11, 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 triseecalis. — 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 vrith 

 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 ribs 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. 



