Mr. S. P. Pratt on some new species of Ammonites. 163 



bercle. The prolongation of the aperture appears to depend 

 upon the growth of the shell, and it varies from a slight pro- 

 jection to 1- inch long; it is concave externally and convex 

 internally. 



2. Ammonites Comptoni. PI. IV. fig. 1. 



Shell discoidal, radiated, the rays alternately two short and 

 one long ; the long rays proceeding from the dorsal to 

 the inner margin, where they become thickened, the two 

 short rays not passing beyond the middle of the volu- 

 tion ; they are curved backwards near the dorsal edge : in 

 the young shell the rays are close, sharp, and slightly 

 elevated; when full-grown the last volution has a few 

 obtuse undulations, but is nearly smooth ; back rounded, 

 with a slight depression in the middle, formed by the 

 nearly meeting rays ; the whole shell without spines or 

 tubercles ; volutions 6 or 7? f rds exposed ; aperture ter- 

 minated on each side with a spatulate projection about 

 1^^ inch long when fully grown, and of similar characters 

 with Am. ElizabetluE. 



3. Ammonites Stufchburii. PI. IV. fig. 2 and 3. 



Shell discoidal, radiated; the rays curved, very regular, form- 

 ing raised lines which reach from the dorsal edge to about 

 the middle of the volution, where they meet a row of 

 small, compressed, distant tubercles, beyond which is 

 another row near the inner margin ; these tubercles vary 

 much in number and relative size ; volutions |rds ex- 

 posed; aperture forming a projecting beak, with waved 

 striae on its surface ; back narrow, marked by the rays 

 passing over it, and terminated on each edge by a range 

 of serrated sharp points formed by the termination of the 

 rays ; volutions exposed, showing both ranges of tu- 

 bercles. 



4. Ammonites Sedgwickii. PI. V. fig. 1. 



Shell discoidal, nearly smooth on the last volution, but having 

 a row of tubercles upon the inner margin ; the spaces be- 

 tween them twice as large as the tubercles : in the young 

 shell sharp raised lines proceed from the rounded back 

 to about the centre of the volution, but do not reach the 

 tubercles ; they become indistinct towards the aperture ; 

 volutions :jth exposed, the last about half the diameter 

 of the shell ; aperture not projecting, forming a well- 

 defined twice-curved termination. 

 M 2 



