COSMOCERAS. 257 



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 a-quarter whorls 

 long. Aptychiis divided, calcareous, very thin, covered with 

 granules on the external surface. Lobes usually deeply divided, 

 siphonal and upper lateral lobe usually of the same length ; a 

 stout auxiliary sutui'al lobe ; lobular bodies narrow. 



Ste2ohanoceras diverges from J^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 representa- 

 tives come from the Oxfordian (Steph. Colliiii, Opp , glomus, 

 0pp.). 



For the forms with contracted aperture, and constricted, 

 sometimes geniculate body-chamber, the name Protojihites^ 

 Ebray, exists, though it appears to me that this separation is 

 not yet well enough established. 



Forty-one Jurassic species. 

 S. ANNULATUM, Sowb. T. 102, figs. 540, 54L 

 S. Blaqdeni, Sowb. T. 102, figs. 550, 551. 



(ienus COSMOCERAS, Waagen. 



Siphonal side mostly with a smooth furrow ; sculpture con- 

 sisting mostly of dividing ribs, directed forwards at the siphonal 

 side, frequently ornamented with nodes or swellings ; margin of 

 aperture in the young state frequently with ears, which are lost 

 by age; body-chamber one-half whorl long. Lobes moderately 

 divided ; siphonal lobe distinctly shorter than the first lateral ; 

 second lateral repeating the form of the first ; one or more aux- 

 iliaries. Aptychus apparently as in Stephanoceras. 



In respect to the limits of this genus, I differ very much from 

 those originally assigned it by Waagen, since I on one hand ex- 

 clude all the cretaceous forms except Cosm. verrucosiim, and on 

 the other include the Parkinsonia ; for the first change the 

 motive may be found in Hoplites above ; the last seems to me 

 necessitated by this, that the whole genus, in our present com- 

 prehension of it, is a complete series of forms, which, with the 

 appearance of the siphonal furrow and development of the sculp- 

 ture, enters upon a line of variation diverging from Stephano- 



