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ventral angle, as seen in Arietites rotiformis, fig. 53. In all the 
species the keel is large and prominent, and accompanied by two 
lateral channels (fig.55). The mouth-border is simple, scooped 
away on the sides, with along, projecting, ventral process. The 
body-chamber is from one to one whor! and a quarter in length. 
The lobes are very characteristic, (Arietites bisulcatus, Brue.) 
The siphonal lobe is nearly as deep as it is broad, and the 
union of its wall with the siphon is nearly in the middle of 
its depth. The principal lateral does not reach to half its 
depth, and is sometimes as broad as it is deep. The lateral 
saddle rises above all the others, and stands upon the ground of 
the principal lateral; in general double the height of the outer 
saddle. The lower lateral is likewise much broader than deep, 
and the columellar is so small that it does not reach to half 
the height or breadth of the saddle, and ends in two branches. 
The Anaptychus is thin, horny, and undivided; in some species 
it has a bell-shaped form. JI have found it so in Arvetites 
semicosatus, Youne, and Arietites stellaris, Sow. 
The genus Arietites, as long ago remarked by Leoponp von 
Bucu, is very characteristic of the Lower Lias, in which we find 
the following species :— 
Arietites Bucklandi, Sow. Arietites rotiformis, Sow. 
" Bonnardi, d’Orb. »  Sauzeanus, d’Orb. 
u Crossii, Wright. » — stellaris, Sow. 
" obtusus, Sow. u Scipionianus, d’Orb. 
” semicostatus, Simp. «»  Conybeari, Sow. 
»  bisulcatus, Brug. «  Brooki, Sow. 
" raricostatus, Ziet. »  Turneri, Sow. 
Genus Harprocrras, Waag.—The 
external outline of the shell of vari- 
ous forms, the ventral area always 
keeled with a round or angular 
border; the sides of the whorls orna-° 
mented with elegant falciform ribs of 
various degrees of thickness. Mouth- 
border sickle-shaped, with lateral 
auricles, and a long, pointed, ventral 
process (fig.57). Body-chamberfron  ** Te Bare ee 
