70 GENESIS OF THE ARIETIDjE. 



Oxyn. Oppeli 1 is a remarkable form, apparently a direct descendant of Gree- 

 noughi, which alone survived in the Middle Lias. 



Note. — I have so far found but few specimens of the Arietidse which could not be identified or properly 

 placed in some genetic series. Two auomalies are in the Museum at Stuttgardt, and both were found in 

 the Angulatus bed. One is somewhat similar to the larger forms of Cat. carusense, and is labelled A mm. 

 bisulcatus. It has a very broad abdomen, the sides of the whorl divergent, the pilas well developed, geniculse 

 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 laticoniatus, Quenst. 



The other specimen is labelled Aiitm. nodosaries, Quenst. It resembles Agas. Scipinnianum in the pilse 

 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 pilse, even on the extreme outer whorl. The three outer whorls 

 alone are preserved, the centre having been destroyed. The pilse 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 geniculse or tubercles were apparent, 

 but the specimen would require cleaning before this could be decisively stated. The pilse 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. 



1 Summ. PL xiii. fig. 16. 



