AMMONITID^. 61 



considerably backwards towards the external margin, entirely 

 disappearing on the siphonal side of the shell. The increase in 

 height of the whorls is very slow. 



Closel}^ related to Arcestes, of which it may be only a sub- 

 genus. 



LoBiTEs, Mojs., 18t3. 



Syn. — Coroceras, Hyatt, 181*7. Clydonites, Lavibe, non Ilauer. 



Bistr. — Nine Triassic species are enumerated. L. deJphino- 

 cephalus, Hauer (xxxvi, 92). L. ellipticus^ Hauer (xl, 58, 59). 



In external form and length of body-chamber agreeing with 

 Arcestes and Didymites. Shell usually with tran verse folds, 

 which are frequently crossed by fine longitudinal striae. The 

 body-whorl frequently assumes a form very different from the 

 inner ones, and not unfrequently closes the umbilicus with a 

 callus. Towards the aperture, however, and always in those 

 forms with a closed umbilicus, there is a constriction which 

 extends forwards in the form of small, projecting, lateral lobes. 

 The sutural lines of the septa consist of entire-margined, high 

 saddles, somewhat contracted at their bases, which vary in height 

 in such a way that the second and fourth are perceptibly lower 

 than would be expected from their position. A high siphonal 

 process. 



In many forms there appears, regularly at the end of the body- 

 whorl and the one next to it, a portion constricted ofl' the 

 "hood;" in other forms the apertui-e is simple, and only pro- 

 longed anteriorly into lobe-like processes at the convex portions, 

 and but little or not at all constricted. 



In Lobites the derivation from the goniatitic ancestry is much 

 more striking than in any other mesozoic genus, inasmuch as 

 the form of the lobes is still completely goniatitic. The ammo- 

 nitic stage is indicated in the structure of the lobes only by the 

 high siphonal process dividing the external lobe. 



Tropilae. 



Shell more or less richly ornamented, provided with radial 

 ribs, which almost always support on the edge of the convex 

 portion (frequently also on the sides) knobs and spinous pro- 

 cesses. Wrinkled layer and impressions of the mantle attach- 

 ments entirely absent. 



Tropites, Mojs., 1875. 



Distr. — 11 Triassic species. Trojntes Ramsaueri, Quenst. (xl, 

 52, 55,56). 



Body-chamber long, embracing one and three-quai"ters to one 

 and one-half whorls. The strong sculpture is interrupted on the 

 convex portion of the shell ; frequently a median keel is present 

 on the same. At the aperture the convex portion is prolonged 



