204 
with a calcareous sheath. Aptychus thick, calcareous, bivalved, 
and folded. Adductor muscles situated near the border of the 
shell in the lower half of the whorl. Suture-line extremely 
ramified. Siphonal lobe mostly shorter than the principal 
lateral, which is large and much branched. The second lateral 
is in like manner well developed, and there are several large 
auxiliaries between the second lateral and the umbilicus. 
Lobe bodies small, with almost parallel borders; lateral lobes 
unequally branched. The genus Oppelia appears first in the 
Lower Oolite, zone of CosmocerasP arkinsoni, as Oppelia subra- 
diata, Sow., and the last representative of the group, as far as 
our knowledge at pregent extends, is in the Upper Jura of 
Stamberg, where a considerable number of different forms are 
found. 
The English species of this genus are not numerous. Oppelia 
subradiata, Sow., from the Inferior Oolite, is a good example. 
Dr. Waacen has figured a number of beautiful forms of 
Oppelia, amounting to twelve species, from the Golden Oolite 
of Keera Hill, near Charee, Kutch, and other higher Oolitic 
beds. ‘“ Oppelia subcostaria, Opp., closely resembles the Euro- 
pean Opp. subradiata, not only in the same form, but even in 
the same varieties as in Europe in the same layer.” (WaAaGEN.) 
Genus Hartoceras, Zittel—The forms included in this group 
have been separated from the genus Oppelia, as they present 
certain characters in common by which they differ from the 
typical lines of that genus; they are all distinguished by a 
narrow umbilicus, a smooth surface, marked with fine lines of 
growth, like Hapl. ooliticum. D’ORB.,; 
from the Inferior Oolite, with its thin 
undivided falciform sculpture which 
passes round the shell. Sometimes 
there are a series of straight parallel 
ribs at intervals, as in Hapl. ligatum, 
D’Ors., between which a number of 
very fine, undivided, smaller and 
thinner folds are placed. The ribs 
are not bifurcated in this genus, and 
Fic; 58.—Haploceras ligatwm, 
d’Orb. 
