MODERN CLASSIFICATION. 
237 
Thysanoid^. 
Thymnoceras cornucopia, Th. Jurense, Th. hircinum, and Th. torulosum, given as 
examples, all belong to the genus Lytoceras. 
Bhacoceras hetero]ihjllum. Sow. = Ex. Phylloceras heteropJiyUim, Sow. 
Phymatoid^. 
Phymatoceras enervatum, Hyatt. 
Ammatoceras insigne, Schubl., and A. variahile, 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. Pelecoceras 
attenuatum, Hyatt. 
HlLDOCERATID^. 
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 serpentinum (PL LIII). 
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 Deutschen geologischen Gesellscbaft,' p. 854, Jalirgang, 1875. 
