VOL. XV. (3) | BUCKMAN—-LIAS AMMONITES 1.233 
Hyatt; A/satetes, Haug. In all these genera the inner 
portion of the suture-line is dependent,—that is it runs 
back and has the lobes pointing across the whorl. This 
feature separates these genera from the family Arietide ; 
they must not be placed as forerunners of the Arietide, 
as Hyatt did; they form a family by themselves, as I 
pointed out’; but the name Psiloceratidz then proposed 
must drop with Pszoceras, so the name CALOCERATID A: 
may be suggested 
The five genera may be easily distinguished :—Pszdono- 
toceras is uncarinate, and has a smooth periphery; in side 
ornament the genus develops catagenically from costate 
to levigate—Ca/oceras is an anagenetic genus, developing 
from smooth to costate to tuberculate, and in periphery, 
from rounded to carinate, to carinatibisulcate—A /sazztes is 
like Caloceras, but has a more complex suture-line— 
Wehneroceras is uncarinate, but the periphery is crossed 
by coste—Schlothermia is a development from the lower 
W ehneroceratan forms, the costz on the periphery becom- 
ing broken until a regular furrow is formed. 
Hyatt divided the Schlothezmze into two subseries ; and 
certainly the dwarf species typified by S. dacunata differ 
much from the Axgulatus-group, suggesting some differ- 
ence in genetic development. Quenstedt proposed the 
generic name Axgulaticeras for the Schlotheimians— 
1883, Schwab. Amm. i, p. 26. If, as seems likely, the 
Schlotheimians are to be further divided generically, 
then Quenstedt’s name, as he selected no type, would be 
available for the group of 4. dacunatus; he mentions that 
as a species of Angulaticeras. 
Hyatt’s idea that P. planordzs is the ancestor of the 
Arietidz, including Schlothezmzq and its allies, cannot be 
accepted. In the first place the peculiar suture-line of 
1 Divisions of so-called Jurassic Time; Quart. Journ. Geol. Soc., vol. liv, p. 445, 
1898. 
