AMMONITIDZ. 67 
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. 
Closely related to Arcestes, of which it may be only a sub- 
genus. 
Loxsires, Mojs., 1873. 
Syn.—Coroceras, Hyatt, 1877. Clydonites, Laube, non Hauer. 
Distr.Nine Triassic species are enumerated. L. delphino- 
cephalus, Hauer (xxxvi, 92). JL. ellipticus, Hauer (xl, 58, 59). 
In external form and length of body-chamber agreeing with 
Arcestes and Didymites. Shell usually with tranverse folds, 
which are frequently crossed by fine longitudinal striz. 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 stphonal 
process. 
In many forms there appears, regularly at the end of the body- 
whorl and the one next to it, a portion constricted off the 
“hood ;” in other forms the aperture 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. 
Tropile. 
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. Tropites Ramsauert, Quenst. (xl, 
52, 55, 56). 
Body-chamber long, embracing one and three-quarters 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 
