346 Dr. FiTTON on the Strata below the Chalk* [App. A. 



Fig. 1 1 . Cyclas media : var. Gibbose ; posterior side rather cuneiform and truncated. It 

 has the appearance of being a little distorted by age. 



Fig. 12. Cyclas angulata. Transversely ovate, convex ; posterior side truncated, and sepa- 

 rated by an angle and a point. A wider, thinner, more transverse, and larger shell than C. media. 



Fig. 13. Cyclas major. (Cyrena, " larger species," Ann. of Phil. N.S. vol. viii. p. 376, et passim.) 

 A convex, smooth shell : — the specimens are generally so imperfect, that their size is almost the 

 only character to be observed. 



Fig. 14. Unto Mantellii. Dorsal and ventral margins nearly parallel, straight; valves flat- 

 tened, twice as wide as they are long ; anterior side small, rounded. 



Fig. 15. Unio subtruncatus. Ovate; valves flattish, thick, with obtuse edges: the posterior 

 extremity obliquely wedge-shaped. 



Fig. 16. Unio Gualterii. Nearly square, with the anterior side rounded ; depressed; marked 

 with twice bent parallel rugae ; posterior side somewhat eared. The only fossil species known 

 that shows to any extent the waved rugae so frequent in the recent species of this genus. The 

 depression in the middle is not constant. 



Fig. 17. Unio Martinii. Ovate, rather convex, nearly smooth, posterior side pointed; um- 

 bones not far from the middle, not prominent. 



Fig. 18. Mytilus Lyellii. Oblong-ovate, somewhat flattened, especially towards the front; 

 convex towards the pointed beaks. 



PLATE XXII. 



Fig. 1. Exogyra bulla. Oblong, convex, nearly smooth ; beaks short, curved. The laterally 

 curved beak distinguishes this shell from the Ostreae of the same beds. Its shape, however, is 

 very variable. 



Fig. 2. Ostrea distorta. (" Ostrea; an undescribed species", Ann. of Phil. N.S. vol. viii. p. 376.) 

 Elongated, narrow towards the hinge ; one valve flat, both nearly smooth. This and the Exogyra, 

 fig. 1. occur in masses, so closely grouped, that the form of the shells can seldom be traced. 



Fig. 3. Bulla Mantelliana. {Bulla, Mantell, Geol. S.E. of England, 249.) A smooth cylin- 

 drical shell, nearly twice as long as wide, truncated at both ends : here accompanied by a small Pa- 

 ludina, supposed to be P. elongata, but which has a smaller spire than that shell generally has. 



Fig. 4. Melanopsisi tricarinata. (Melania tricarinata, Ann. of Phil. N.S. vol. viii. p. 376.) 

 Subulate, conical ; whorls seven, carinated. Three carinae occupy the exposed portions of the 

 whorls, and are crossed by distinct lines of growth ; the central one is the most prominent. More 

 perfect specimens have induced me to remove this from the genus Melania to Melanopsis. 



Fig. 5. Melanopsisi attenuata. Subulate, elongated ; whorls about nine ; with several carinae 

 crossed by undulations, strongest at the upper part of each whorl. The length is in proportion 

 greater, and the whorls more numerous than in the last species, fig. 4. 



Fig. 6. Paludina Sussexiensis. Spire an elongated cone, with nearly straight sides ; whorls 

 five, smooth, more numerous than in either P. Jluviorum, lenta, or carinifera of Min. Conch. 

 There are, probably, several other species of Paludina in the Wealden strata. 



Fig. 7. Nerilina Fittonii. (Mantell, Geol. S.E. of England, p. ^48.) Convex; tricarinated ; 

 aperture large ; spire very small. The specimens do not show the aperture, and are hardly suf- 

 ficient to prove this shell to be a Neritina rather than a Nerita. The lowest figure is magnified. 



Fig. 8. Tornatella Popii. Elliptical, pointed, smooth ; spire small, of about three whorls. 

 The cast shows two plaits upon the columella. Named from the Rev. W. L. Pope, of Tonbridge 

 Wells. 



