47i 



THE LIAS AMMONITES. 



The border of the aperture is encircled either by a broad band as in Steph. commune, 

 or lateral lappets are produced and inflected as in Steph. Braikenridgii, in which they are 

 often conspicuous and well preserved (figs. 198 and 199). In Steph. Blagdeni, Steph. 

 Humphriesianum > and Steph. Deslongchampsii the mouth is encircled with a broad band. 

 The body-chamber varies from one half to one and a quarter whorls in length. The 

 suture-line is much ramified. The siphonal and principal lateral lobes are nearly of 

 equal length ; the inner lateral is much smaller and there are several auxiliary branches. 



Fig. 199. — Stephano- 

 ceras Braikenridgii. 



Pig. 200. — Stephanoceras 



£ 



M 



Fig. 201. — Stephanoceras 

 Blagdeni. 



FIG. 202.— Stephanoceras 

 Deslongchampsii. 



Many characteristic species appear for the first time in the Upper Lias, as Steph. 

 commune, Step/t. annulatum, Steph. crassum, Steph. fibulatum, and Steph, subarmatum. 

 The zone of Steph. Humphriesianum in the Inferior Oolite is a great depository of the 

 species of this genus both in England and in France. In this horizon we find — 



Stephanoceras Braikenridgii, Sow. 

 Brocchii, Sow. 



— Brongniarti, Sow. 



— coronatum, Briig. 

 Blagdeni, Sow. 



Stephanoceras Deslongchampsii. 



— Gervillii, Sow. 



— Humphriesianum, Sow. 



— Sauzei, d'Orb. 



— linguiferum, d'Orb. 



The Aptychus is bivalved, calcareous, and very thin, and has upon its external surface 

 numerous small granules. 



The genus Stephanoceras appears to have certain near relations with the genus 

 Aegoceras through the species Aeg. pettos of the Middle Lias (see p. 363). 



The group represented by other Jurassic forms, as Stephanoceras modiolare, Luid., 

 and Stephanoceras macrocephalum , Schloth., stands well apart from the more compressed 

 forms of Harpoceras in the Upper Lias. All the varieties of the Macrocephali are 

 globose from the extreme involution of the spire and the narrowness of the umbilicus ; 

 they also possess a remarkably complicated suture-line. This genus has very few 

 forms in the European Jurassic rocks and occupies a limited horizon in them, 

 commencing with Stephanoceras macrocephalum in the Cornbrash of England and 



