MODERN CLxiSSIFICATION. 237 



Thysanoid^. 



Thysanoceras cornucopia, Th. Jiirense, Th. hircinmn, and Th. torulosum, given as 

 examples, all belong to the genus Lytoceras. 



Bhacoceras heteropliyllum. Sow. = Ex. Phylloceras heterophylhm, Sow. 



Phymatoid^. 



Phymatoceras enervatum, Hyatt. 



Ammatoceras insiyne, Schubl., and A. variabile, d'Orb. — These species had been 

 already referred to the genus Hammatoceras, and placed, through an oversight of the 

 author, in the Middle Lias. 



Genus Pelecoceras, Hyatt. — This genus is not well defined. Felecoceras 

 attenuatum, Hyatt. 



HiLDOCERATIDiE. 



Genus Hildoceras, Hyatt. — Abdomen keeled and channelled ; pilae large and 

 broad. Young with first whorl smooth. Ribs, keel, and channels appear on the second 

 whorl. The ribs begin as folds, and bend, as in the adult, but with the abdominal bend 

 inclined more towards the apex. Ex. Harpoceras bifrons, Brug. (PI. LIV)=:^. Walcotii, 

 Sow., which our author makes a distinct species : H. Walcotii is the true H. bifrons, Brug. 



Genus Grammoceras, Hyatt. — Abdomen keeled, but not channelled ; whorls 

 flattened laterally giving a discoidal aspect to the shells. Ribs finer and less prominent 

 than those of Hildoceras. The young also continue smooth much longer, and channels 

 never appear. Ex. Harpoceras serpentinuni (PI. LHI). 



Genus Leioceras, Hyatt. — Abdomen keeled, acute ; sides of the whorls flattened ; 

 envelopment uniformly greater than in Grammoceras Ex. Leioceras opalinum, Rein. 



Professor M. Neumayr, of Vienna, has contributed an important memoir, ' Die 

 Ammoniten der Kreide, und die Systematik der Ammonitiden," in which is brought into 

 a continuous and connected form the progressive stages which the systematic study of 

 Ammonites has made in the hands of the younger palaeontologists of the German 

 school since the time Professor Suess called their attention to the subject, in his classical 

 memoir ' Ueber Ammoniten,' already cited in these pages. The works of Waagen, 

 Mojsisovics, Hauer, Zittel, Laube, and his own important papers have all been put under 

 contribution to bring the subject up to our present stand-point of knowledge. The 

 Ammonites are grouped into four families : 



1 ' Zeitschrift der Deutsclien geologischen Gesellscliaft,' p. 854, Jalirgang, 1875. 



