400 A. H. Foord — Ammonites in the British Museum. 



founded upon broken shells of Ancyloceras (q. v.) ; but the discovery 

 of the aperture has dispelled this error. There is no doubt, however, 

 that Toxoceras is nothing more than a fragment of Crioceras. Ancy- 

 loceras begins like Crioceras, but at the last whorl the shell is 

 straightened out at a tangent to the coiled part, and after attaining 



Fig. 21. 



Crioceras Bmerici, Leveille. (JSTeocomian.) 



a considerable length in a straight course it bends over abruptly 

 in the direction of the coiled part, as in ScapJiites. Crioceras and 

 Ancyloceras are variously and elegantly ornamented with ribbing, 

 spines, and tubercles. Crioceras extends from the Neocomian to 

 the Upper Greensand; Ancyloceras from the Inferior Oolite to the 

 Chalk. 



Fig. 22. 



Ancyloceras Matheronianum, d'Orb. (Neocomian.) 



Section II. — This section includes Ammonites of flat, disc-like 

 form, with Ceratites-Yvke; sutures and deeply embracing whorls. 

 SpTienodiscus and Buchiceras (Upper Cretaceous) are characteristic 

 genera. Placenticeras (Cretaceous) includes such species as P. Largil- 

 lertianum and P. Orbignyanum. 



An hour spent in this gallery will well repay the student interested 

 in the study of the fossil Cephalopoda. 



