80 AMMONITID^. 



discoidal, spiral shell, and evolute, with discoidal, helicoid or 

 straight shell, the whorls unwound partly or entirely. This 

 evolution is partly generic, but in some instances is known to be 

 accidental: thus specimens of Acanthoceras angidicostatum, d''0v}3. 

 have the whorls slightly embracing, or merely in contact (Lj^to- 

 ceras), or completely detached (Crioceras). 



a. Normal. 

 Stephanoceras, Waagen, 1869. 



Sy7i. — Dactylioceras, Hyatt, ISGt. Globites, de Haan, 1825. 

 Orbulites, Lam., 1801. Sphseroceras, Bayle, 18*78. 



Dintr. — 41 Jurassic sp. S. (Dactylioceras) annulatum, Sowb. 

 (xxxiv, 41, 48). S. Blagdeni, Sowb. (xxxiv, 51, 59). 



Greneral form of the shell ver}^ variable, external side rounded 

 without keel, angle or furrow. Sculpture never sickle-shaped, 

 decorated with straight, bifurcating ribs, abundantly provided 

 with nodes or swellings. Margin of aperture simple or with ears 

 mostly formed of a broad, smooth zone ; aperture frequently 

 constricted. Body-chamber one to one and one-quarter whorls 

 long. Lobes usually deeplj^ divided, siphonal and upper lateral 

 lobe usually of the same length; a stout auxiliary sutural lobe; 

 lobular bodies narrow. Aptychus divided, calcareous-, very thin, 

 covered with granules on the external surface. 



Stephanoceras diverges from ^goceras with Steph. pettos in 

 the middle Lias ; according to the subdivision into groups, it 

 embraces the Liassic Planulata, Coronata and Bullata after the 

 exclusion of some heterogeneous elements ; the last represen- 

 tatives come from the Oxfordian {Steph. Gollini, 0pp., gloinus, 

 0pp.). 



CADOCERAS, Fischcr, 1882. Shell much swollen; umbilicus 

 narrow, carinated ; last whorl entirel}" smooth, preceding whorls 

 with ribs forming an angle directed forwards in the ventral 

 region. S. modiolare^ Luid. 



PROTOPHYTES, Ebray , 1860. Last whorl geniculated, embracing ; 

 umbilicus transverse, linear ; ribs interrupted at the periphery ; 

 aperture with a peripheral appendage, triangular, wide and thick. 

 S. Oxfordianum^ Ebray. 



(ECOPTYCHius, Neumayr, 1878. Last whorl geniculated, em- 

 bracing ; lateral ear-like projections short and narrow ; a cowl-like 

 ventral appendage. Q^. refractus^ de Haan. 



MORPHOCERAS, Douville, 1880. Whorls rounded with radiating 

 ribs uniting in groups of one to three near the umbilicus, which 

 is scalariform in the juvenile, and much widened in the adult; 

 aperture geniculated, almost completely closed by the expansion 

 of the lateral ears, which unite at the median line on one side 

 and on the other touch the preceding whorl ; thus there are, so 

 to say, five apertures, the peripheral, two small ones, placed each 



