Geol.— Vol. I.] SMITH— COMPARATIVE STRATIGRAPHY. 383 



Waagen's (38) monograph was the first to give a compre- 

 hensive, elastic, and exact definition of the genus Ceratites, 

 and even his work was based entirely on Asiatic species, 

 which depart considerably from the Germanic prototypes. 

 Dr. A. Tornquist was the first to make a systematic com- 

 parison of the Germanic ceratites with those of the Alpine 

 and other groups, and to him is due the reestablishment of 

 the group of the Nodosi in its real importance as the typical 

 and normal forms. 



This group embraces forms of moderate involution, not deeply embracing, 

 but increasing rather rapidly in diameter, thus causing the umbilicus to be 

 wide. The whorls are subquadrate in cross-section, usually higher than wide, 

 with square abdominal shoulders and somewhat flattened venter. The 

 sculpture consists of ribs starting out from the umbilicus, and running nearly 

 straight up the sides, either single or bifurcating. These ribs do not usually 

 extend beyond the abdominal shoulders, which separate the sculptured sides 

 from the ventral portion usually destitute of all sculpture, except in a few 

 groups where there is a low ventral ridge. The umbilical and abdominal 

 shoulders are often provided with strong knots, which may also occur on the 

 lateral ribs; these knots, however, are not set close together as in Balatonites 

 and Trachyceras. 



The septa consist of rounded saddles and serrated lobes, and in the more 

 specialized forms even the saddles may be denticulated. The external lobe 

 is divided by a siphonal saddle into two narrow branches; there are two 

 laterals, and a series of several small auxiliaries, which may be reduced to 

 mere denticulations of a nearly straight saddle. The internal (antisiphonal) 

 lobe is long, narrow, and bifid, flanked by a lateral and an auxiliary series, 

 corresponding closely to the outside septa. The body-chamber is rather 

 short, not more than three-quarters of a revolution in length. 



Ceratites has the greatest resemblance to Hiingarites, 

 from which it differs in the rugose sculpture, the greater 

 evolution, the absence of abdominal shoulder keels, and the 

 almost total absence of a true ventral keel. The two genera 

 agree exactly in septation, and this resemblance indicates 

 their kinship. 



Hungarites is the older and more primitive form, and 

 may be the ancestor of Ceratites, although this is not likely. 

 E. von Mojsisovics has always regarded Dinarites as the 

 radicle of the group, but this genus appears not to have 

 existed in the older part of the Lower Trias, in beds older 

 than those containing Ceratites, while Hungarites occurs 



