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from its sides. In England Peltoceras athleta, Pur., and 
Peltoceras Williamsoni, Pum. represent this genus; both species 
are limited to the Oxfordian strata. 
Genus Simoczras, Zitt—Shell flat, discoidal, with a wide 
umbilicus, ventral side rounded or channelled. Sculpture 
seldom absent, and consisting for the most part of straight 
simple or divergent ribs, which in general, during the entire 
life of the species, or at any rate during youth, are unbroken 
on the ventral side, and abundantly provided with tubercles. 
They have the last whorl much swollen out; body-chamber 
three-fourths of a whorl; mouth-border in geologically young- 
est forms with upward bent external auricles, in older forms 
unknown. The lobe-line is not complex; siphonal lobe the 
largest ; external saddle broad, and much developed. Suteral 
lobes very small; and single pointed. This genus is found only 
in the uppermost division of the Jurassic rocks, commencing in 
the upper part of the Middle Jura, and extending upwards into 
the lower Tithonian or uppermost Jura. Simoceras anceps, 
Reu., and Simoceras Frassi, Orv., are types of this genus. 
The Author desires to return his best thanks to his old friend, 
the Rev. Tos. WittsHire, F.G.S., the Secretary, and the 
Council of the Paleontographical Society for their kind 
permission to use the wood-cuts out of his Monograph 
published by them for the purpose of illustrating this 
memoir. 
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