250 
THE LIAS AMMONITES. 
Inferior Oolite. 
Harpoceras Murchisonse, Sow. 
— Tessoniaiium, d'Orb. 
Harpoceras Sowerbyii, Mill. 
— Edwardianum, d'Orb. 
Genus Oppelia, Waag. — Shell discoidal and liiglily involute ; umbilicus very 
small ; whorls much elevated. Ventral edge either more or less acute, or rounded, "on 
different portions of its extent. Sculpture slightly falciform, with a double set 
of ribs on the sides. Body-chamber sometimes ribbed, neither keeled nor angular; 
from one half to two thirds of a whorl in length. Mouth-border falciform, sometimes 
Avith auricles, always having round external lappets. Siphuncle large, with a calcareous 
sheath. Apiychus 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 O-ppelia appears first in the 
Lower Oolite, zone of Cosmoceras Parkinsoni, as Oppelia subradiata, Sow\ ; and the last 
representative of the group, as far as our knowledge at present 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. Waagen 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 stibcostaria, 0pp., closely 
resembles the European 0pp. subradiata, not only in form, but even by similar varieties, 
as in Europe, in the same stratum " (Waagen). 
Genus Haploceras, 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 passing round the shell. Sometimes there 
are a series of straight parallel ribs at intervals, as in Hapl. ligatum, 
fig. 156, between which a number of very fine, undivided, smaller, 
and thinner folds are placed. The ribs are not bifurcated in this 
genus, and there is neither a keel nor a channel in the siphonal 
area. The body-chamber is short and the structure of the 
Fig. x'iifi.— Haploceras Aptyclius unkuowu. The numbcr of the lobes is variable. In 
itgatxmi. Or . addition to the siphonal lobe and the principal and smaller laterals. 
