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 Stephanoceras, 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, Prom 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. Fig. 159. Fig. 160. 
Stephanoceras Blagdeni, Sow. Stephanoceras Brackenridgii, showing labial prolongation. 
In Siep/i. Blagdeni (fig. 157), and Steph. Hiimphriesianum, 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. anmdatum. Sow. (fig. IGl), 
and Stejjh. commune (fig. 162), with Steph. crassum, Steph. jitjidat urn, and Steph. HoUandrei, 
all from the same beds. The zone of Steph. Humphriesiamm, Inferior Oolite, is one great 
depository of the species both in France and England. We have the following list 
therefrom : 
