BLUE CHALK MARL. 91 



The specimen represented (tab. xxi. fig. 3) is from Eingmer ; the shell 

 is nearly entire, and most beautifully iridescent. 



18. Ammonites lautus. Tab. xxi. fig. 11. {Geolog. Trans, vol. v. p. 58.) 

 Involute, depressed, volutions inserted, transversely radiated, radii strongly 

 curved, arising in pairs from a row of oblique ridges on the inner margin, 

 and terminating with intermediate rays on the outer edge : carene deeply 

 channelled, bordered by alternating compressed tubercles ; dissepiments 

 very foHaceous. 



The volutions are three or four in number, and two-thirds concealed. 

 The rays arise in pairs from the ridges of the inner edge, and being joined 

 by one or two intermediate ones, proceed with an elegant sweep to the 

 outer margin, where they terminate in obtuse flattened tubercles, ge- 

 nerally three or four to each tubercle. The carene is deeply channelled, 

 the edges serrato-tuberculate, the tubercles being disposed alternately. 

 The aperture is obscurely sagittate, and equal in length to half the dia- 

 meter of the shell. The situation of the siphunuclus is unknown. 



This species resembles A. auritus (of Sowerby), but is distinguished by 

 its prominent curved rays, by the ridges on the inner volution being less 

 tubercular, and the inner volutions two-thirds concealed. It occurs at 

 Laughton, Ringmer, and NorUngton. 



The figure is from a specimen in which the shell is entire. 



19. Ammonites biplicatus. Tab. xxii. fig. 6. 



Depressed, slightly umbiUcate ; volutions inserted, transversely radiated ; 

 rays prominent, curved, bifurcated, arising from a row of oblong projections 

 on the inner edge of the volutions, and terminating in tubercles on the 

 outer margin ; carene flat, bordered by alternating, compressed tubercles. 



The volutions are tliree or four, the tubercles on the inner margin 

 distinct, each giving origin to a pair of rays that terminate in a tuber- 

 cular projection on the edge of the keel. The inner volutions are two- 

 thirds concealed, the inner row of tubercles alone being visible. The carene 

 is nearly flat between the tuberculated margins by which it is bordered. 



The aperture is obtusely sagittate, and its length rather less than half 

 the diameter of the shell. 



N 2 



