MODERN CLASSIFICATION. 
225 
band is more voluminous, and in like manner, as the mouth was developed onwards, the 
receding band formed the ribs and tubercles so well shown in that Ammonite. In 
Stephan. Brailcenridgii the sides of the border develop long, inflected, lateral lappets, 
which bend over the aperture, as seen in figs. 117 and 118. A like form of mouth- 
border is seen in the shells of Stephan. Sauzei and Stephan. linguiferum, and a still 
more marked variation of the lateral lappets is found, in Stephan. Gervillii, Stephan. 
Brongniartii, all derived from the Stephanoceras Himphriesianum zone of the Inferior 
Oolite, and Stephan. bitllatum, from the Great Oolite. 
In Cosmoceras the sides are often highly ornamented with ribs and tubercles, which 
bespeak a corresponding development in the mouth-border of the shell. In Cosmoceras 
Jason (fig. 119) the lateral processes are very long, equalling two thirds the diameter of 
the last whorl. Many years ago a large number of this species were collected from the 
Oxford Clay near Chippenham, in a very perfect state of preservation, with the body- 
chamber and mouth-border complete. In other species of this group I have not been 
fortunate in finding the termination of the shell. 
Fig. 119. Fig. 120. Fig. 121. Fig. 122. 
Cosmoceras Jason, Reinecke. Hoplites mammillaris, Schloth. Hoplites Martini, d'Orb. 
In Hoplites mammillaris (figs. 120, 121) we have another example showing how the 
remarkable ornamentation of some of the shells of this group depends on the develop- 
ment of the mouth-border. Here the ridges with their spines, and the valleys with 
their smooth surface succeed each other, owing to the advance of the calcareous oral band, 
and its temporary cessation of growth, producing the remarkable form of shell this species 
assumes (fig. 120). A similar condition of the mouth-border has formed the ornamented 
shell of Hoplites Mai'tini (fig. 122), which I have collected in the Lower Greensand 
(Neocomian) from the Atherfield section, Isle of Wight. 
In Lytoceras the mouth is circular and without lateral processes : the shell is 
distinguished especially among its Liassic forms for the reticulate structure of the test 
and the prominent frills that are developed at intervals, as in Lytoceras fimJjriatiim 
(fig. 123). These fimbriae originated from a periodic activity in the secreting power of the 
30 
