Ammonoidea. 



41 



■whicli they are ornamented. A few examples will serve as 

 illustrations, viz.: Stephanoceras Blag dent {Yi^. 72), Inferior Oolite, 

 Stephanoceras coronatum (Fig. 73) and Costnoceras Jason (Pig. 74), 

 of the Callovian or Oxford Clay, and Hoplites radiatus (Fig. 75), 

 of the Neocomian. Another characteristic shell of this group is the 

 Acanthoceras Rhotomagense of the Lower Chalk. 



A small group of forms still remains to be considered whose 

 structure (external and internal) has led to their being regarded 

 as offshoots from the Stephanoceuatid^. They may be divided 

 into two sections — the first consisting of shells partly uncoiled ; 

 the second, in which the shells are completely coiled, with 

 deeply embracing whorls. 



Section I. — The form of Scaphites (Fig. 76) immediately recalls 

 that of Macroscuphiles, but it diff'ers in several particulars : it is 



GALLERY 



VII. 

 Wall-cases 

 5, 9, 10 ; 

 Table - 

 cases 62-8; 

 Table-case 

 62. 



Fig. 76. — Scaphites Sugardianus, D'Orb. Fig. 77. — Criocerm Umerici, Leveille. 

 Cretaceous. Neocomian. 



much more closely coiled, that is, the inner coils of the shell are 

 not seen, being covered up by the succeeding ones ; and further, 

 the uncoiled part is much shorter and its outline more rounded, 

 while it bends over so as to almost reach the coiled part. Table- 

 Scaphites is abundant in the Middle and Upper Cretaceous, case 61. 

 Crioceras has the form and curvature of an Ammonite, but the 

 whorls are not in contact (Fig. 77). It was formerly supposed 

 that this genus was wrongly founded upon broken shells of 

 Ancyloceras {q v.) ; but the discovery of the aperture has dis- 

 pelled this error. There is no doubt, however, that Toxocera& 

 is nothing more than a fragment of Criocerm, Ancyloceras begins 



