SECOND, OR SCHLOTHEIMIAN BRANCH. 125 
TMAGOCERAS. 
Tmaegoceras latesulcatum, Hyarr. 
Amm. latesulcatus, HAvER, Ceph. d. Lias, d. Nordéstl. Alpen, pl. ix. fig. 1-3. 
This extraordinary form, found in the red limestones of Adneth, has a combi- 
nation of characteristics altogether distinct from that-of any other species. The 
form of the whorl, its smooth shell, and the discoidal mode of growth, are purely 
psiloceran. The sutures are, however, arietian, and more like those of Caloceras 
than typical Psiloceras or those of any other genus. We are not aware of its 
having been found elsewhere than in the Mediterranean province. Hauer 
appears to think that its affinities may lie with the Arietidx, and that is also our 
opinion, but until the young have been studied it cannot be classified. 
Tmaegoceras levis, Hyarr. 
Ariet. Levis, GEYER, Ceph. v. Hierlatz b. Hallstadt, pl. iii. fig. 10. 
This is a smooth, keeled, and channelled discoidal form like the preceding, 
but dwarfish, like other species of this locality. 
PLICATUS STOCK. 
SECOND, OR SCHLOTHEIMIAN BRANCH. 
The living chamber is of uncertain length, though Quenstedt gives it in his 
«¢ Ammoniten des Schwiabischen Jura” as possibly a volution in length in Schlo- 
theimia. The shell is involute in some forms. The whorl is flattened laterally, 
and in old age became subacute. A smooth median zone or channel was formed 
on the abdomen by the suppression of the piles, which were continuous across the 
abdomen in the preceding nealogic or ephebolic stages. There are no geniculs, 
though the pile are very completely developed. The forward bend is necessarily 
gradual, the whorl never having a sufficiently quadragonal form for the forma- 
tion of abrupt bends or genicule on the edges of the abdomen. The sutures 
resemble those of Psiloceras and Caloceras. 
W A HNEROCERAS.? 
The adult has a smooth median zone along the abdomen. The pilm, so far as the 
young are known, cross the abdomen during the earlier nealogic stages, and this 
character is retained throughout the adult stages in some species. The smooth zone 
is really an incipient channel, formed subsequently by the resorption of the pile. 
This process may take place either in the later nealogic, ephebolic, or senile stage, 
according to the species. In old age the pile tend to degenerate into folds, and 
1 Tunyos, a furrow. 
2 Dedicated to Dr. Frantz Wahner, as a token of respect for his remarkably accurate and instructive 
researches upon the Arietidae. 
