208 
one half to two thirds of a whorl in length. Suture-line 
moderately ramified. Siphonal lobe short and bifurcate, with 
divergent branches always shorter than the principal lateral, 
which is largely ramified. The second lateral much smaller 
than the principal, and passing inwards into several auxiliaries. 
The Aptychus bivalved, thin, and calcareous, with a shelly 
covering and several longitudinal folds, as seen in Harp. Levisom, 
Simp. ; 
Harpoceras first appears in the Middle Lias, in the zone of 
Aeg. Jamesoni ; it attains its highest development in the Upper 
Lias, and is found in the Lower and Middle Jurassic rocks, 
disappearing in the Upper Kimmeridgian with Harp. Zio. Orr., 
collected from the zone of Pteroceras oceani, at Mahringen, near 
Ulm, Wiirttemberg. 
Mippie Liss. 
Harpoceras, nov. sp. Harpocerasimpendens, Y oung & Bird: 
" ‘ Normanianum, d’Orb. " arietiforme, Opp. 
Urrer Litas. 
Harpoceras serpentinum, Rein. Harpoceras insigne, Schibl. 
u Levisoni, Simp. ", opalinum, Rein. 
" bifrons, Briig. " radians, Rein. 
0 falciferum, Sow. " striatulum, Sow. 
" Lythense, Young. " Aalense, Ziet. 
" ovatum, Young. ” Thouarsense. d’Orb. 
" variabile, d’Orb. ut primordiale, Schloth. 
InFERIOR OOLITE. 
Harpoceras Murchison, Sow. Harpoceras Sowerbyii, Mill. 
a Tessonianum, d’Orb. " Edwardianum, d’Orb. 
Genus Orrrtta, Waag.—Shell discoidal and highly involuted ; 
umbilicus very small; whorls much elevated. Ventral side 
either upon the chamber or upon all the whorls more or less 
acute and rounded. Sculpture slightly falciform, with a double 
set of ribs on the sides. Body-chamber sometimes ribbed, 
neither keeled or angular; from one half to two thirds of a 
whorl in length. Mouth-border falciform, sometimes with 
auricles, always having round external lappets. Siphon large, 
Q 2 
