MODERN CLASSIFICATION. 



251 



there are from two to four auxiliaries present. The ramifications of the principal laterals 

 are not symmetrically divided ; and in the forms from the Neocomian strata the lobes have 

 a more simple structure than in those found in the Upper Cretaceous. This genus has 

 a very wide stratigraphical range from the Lower to the Uppermost stages of the Jurassic 

 series, and likewise in the Neocomian and Upper Cretaceous formations. 



Genus S tephanoceras, Waag. — The general form of the shell is very variable in this 

 genus ; the ventral side is in general large and round, without keel, border, or channels. 

 The sculpture is often highly ornamental. From the suture rises a short, stout rib, 

 which often ends in a tubercle at the middle of the side. From the tubercle two or three 

 smaller ribs arise, which pass over the ventral surface and unite with their fellows from 

 the opposite side. Sometimes the tubercles are wanting, and a number of fine encircling 

 ribs make up the entire sculpture. 



The mouth-border is often provided with broad lateral lappets, which are produced 

 and inflected, as in Stephanoceras Brackenridgii (fig. 159), where they are very con- 

 spicuous, and often well preserved. 



Fig. 157. Fig. 158. 



Stephanoceras Blagileni, Sow. 



Pig. 159. Fig. 160. 



Stephanoceras Brackenridgii, showing labial prulongation. 



In Steph. Blagdeni (fig. 157), and Steph. Humphriesianum, the mouth is encircled by 

 a thick band, from whence the strong ribs in these species is derived. The body-chamber 

 is from one 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 lower lateral is 

 much smaller, and there are several branched auxiliaries. There is considerable diversity 

 among the species. The genus Stephanoceras appears to have a certain family relationship 

 with the sub-group Involuti of the genus Aegoceras of the Middle Lias. Many characteristic 

 species appear for the first time in the Upper Lias, as Steph. annidatum. Sow. (fig. 161), 

 and Steph. commune (fig. 162), with Steph. crassmn, Stejjh.fihulatum, and Steph. Hollandrei, 

 all from the same beds. The zone of Steph. Humphriesianum, Inferior Oolite, is one great 

 depository of the species both in France and England. We have the following list 

 therefrom : 



