TRACHYCERAS, CHORISTOCERAS, ETC. 245 



tiuguished bj their broad saddle stalks, with divisions cut in 

 obliquely, the oblique position of the tips of the lobes, great de- 

 velopment of the principal lobes, and striking reduction of 

 auxiliary ones. 



Eleven Triassic species. 

 Tropites Ramsaueri, Quenst. T. Ill, figs. 655-657. 



Genus TRACHYCERAS, Lauhe. 



Body-chamber short, one-half to two-thirds of a whorl long. 

 The sculpture on the convex portion is interrupted ; in the geo- 

 logically younger forms a more or less deep median furrow is 

 sunken in, at which the ribs terminate in a tubercle. Aperture 

 with a short lobate process on the convex portion. Loljes agree- 

 ing with Tropites ; much simpler in the geologically older forms. 



Sixteen Triassic species. 

 TRACHYCERAS BicRENATUS, Hauer. T. 109, figs. 641, 642. 



Genus CHORISTOCERAS, Hauer. 



From Trachyceras a group branches off", distinguished by a 

 larger growth and simple or slightly toothed lobes, with a short 

 body-chamber, in which, on the inner whorls the median inter- 

 ruption of the sculpture on the convex portion is almost alwa3's 

 visible, whilst on the outer whorls the ribs are continuous over 

 the convex portion. It is also to be observed that on one hand 

 the lobes exhibit the persistence of an ancient stage of develop- 

 ment, and on the other a special variation from the sculpture of 

 the Trachyceras type. 



Nine Triassic species. 



Genus RHABDOCERAS, Hauer. 



Rod-like, elongated forms with oblique annular sculpture and 

 simple curved lobes ; still very imperfectly known, and are, ac- 

 cording to all probabilitj^, to be placed next to Choristoceras. 

 Rhabdoceras Suessii, Hauer. T. 100, figs. 513, 514. 



Genus COCHLOCERAS, Hauer. 



The whorls are spirally coiled to the left, with continuous 

 ribs and simple curved lobes. This form also may be placed 

 next to Choristoceras. 

 Cochloceras Fischeri, Hauer. T. 100, figs. 518, 519. 



