SECOND, OR SCHLOTHEIMIAN BRANCH. 125 



TMAEGOCERAS. 1 

 Tmaegoceras latesuleatum, Hyatt. 



Aram, latesulcatus, Hauer, Ceph. d. Lias. d. Norddstl. Alpen, pi. 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 Arietidse, and that is also our 

 opinion, but until the young have been studied it cannot be classified. 



Tmaegoceras levis, Hyatt. 



Ariel. Levis, Geyek, Ceph. v. Hierlatz b. Hallstadt, pi. 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 Schwabischen 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 pilse, which were continuous across the 

 abdomen in the preceding nealogic or ephebolic stages. There are no geniculas, 

 though the pilae 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 geniculaa on the edges of the abdomen. The sutures 

 resemble those of Psiloceras and Caloceras. 



WiEHNEROCERAS. 2 



The adult has a smooth median zone along the abdomen. The pilae, 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 piloe. 

 This process may take place either in the later nealogic, ephebolic, or senile stage, 

 according to the species. In old age the pike tend to degenerate into folds, and 



1 Tyijyos, a furrow. 



2 Dedicated to Dr. Frantz Warmer, as a token of respect for his remarkably accurate and instructive 

 researches upon the Arietidse. 



