70 GENESIS OF THE ARIETIDA. 
Oxyn. Oppeli' is a remarkable form, apparently a direct descendant of Gree- 
noughi, which alone survived in the Middle Lias. 
Nore. —I have so far found but few specimens of the Arietide which could not be identified or properly 
placed in some genetic series. ‘Two anomalies are in the Museum at Stuttgardt, and both were found in 
the Angulatus bed. One is somewhat similar to the larger forms of Cal. carusense, and is labelled Amm. 
bisulcatus. It has a very broad abdomen, the sides of the whorl divergent, the pile well developed, geniculee 
prominent and straight. The keel is low and angular, and two sulcations on either side stretch to the 
incurved edges of the abdomen and these edges form two ridges as prominent as the keel itself; the sutures 
are similar to those of Vermiceras. It may be an extreme form of Caloceras, allied to Cal. Haueri, but is 
apparently not allied to Jaticostatus, Quenst. 
The other specimen is labelled Amm. nodosaries, Quenst. It resembles Agas. Scipionianum in the pile 
and tubercles, the absence of channels, prominent keel, and helmet-shaped outline of the whorl in section. 
The superior lateral saddles are narrow and deep, the superior lateral lobes also very narrow, long, bifid, 
and deeply divided by a terminal marginal saddle. The inferior lateral saddles are deep, and occupy nearly 
the entire breadth of the sides of the whorls, and have deep, rounded marginal saddles. 
In the Museum of Amherst, Mass., there is also an enormous shell, which had reached the large size 
of 600 mm. Though undoubtedly very old and much compressed, it had not yet suffered the loss of its 
keel, which is plainly apparent, nor the pile, even on the extreme outer whorl. The three outer whorls 
alone are preserved, the centre having been destroyed. The pile are about 20 mm. apart on the outer 
whorl, and have depressed folds. They are more prominent and about 10 mm. apart on the second 
inner whorl, and about 5 mm, apart on the innermost whorl. No genicule or tubercles were apparent, 
but the specimen would require cleaning before this could be decisively stated. The pile were slightly bent 
forward, and fold-like, as in Caloceras. On the umbilicus were two fossil shells, said to be Plagiostoma 
gigantea, and the locality where it was found was Dorsetshire, England. The outer whorl was 110 mm. in 
the abdomino-dorsal diameter, and the slow increase and evidently large number of whorls in the full 
grown shell, as well as the rotund form of the sides of the whorls and the slight amount of involution and 
extremely discoidal aspect, indicated a species of either Caloceras or Vermiceras. 
7 Sumin. Pl, xiii. fig. 16, 
