1876.] 393 [Hyatt. 



distinguishable from the typical Gervilii, except by the coarseness 

 of the ribs and the size. There are several fine specimens in Quen- 

 stedt's collection, also, which show this very plainly. 



There is a very remarkable series «of specimens, undoubtedly be- 

 longing to this species, which are described by Quenstedt' as a fine 

 ribbed variety of Humphriesianum. They have no tubercles except 

 at an early age in Brown Jura " y." The forms in " d " directly con- 

 nected with these, show the tubercles even less prominently, while 

 those in " e ' are smooth, like the young of macrocephalum. All 

 have the rapid increase by growth in the size of the shell, which is 

 so characteristic of Brocchii, as well as the fine ribs and narrower 

 umbilicus. They appear to show a direct connection with Steph. 

 Herveyi, but are, in reality, only representative forms, which are 

 direct descendants of Brocchii, and resemble macrocephalum in the 

 young because of their accelerated development of the ancestral 

 characteristics, leading to the gradual suppression of the Pettos-like 

 form and characteristics which they inherited in a modified form 

 from contractum. 



Some specimens in the British Museum have very coarse lateral 

 ribs, and others the finer ribs of the specimens which resemble con- 

 tractum in the young. The specimens in the Bristol Museum attain 

 a very large size, and in the largest the last whorl or two becomes so 

 contracted and flattened laterally, that it resembles the forms of the 

 Perisphinctes group. 



Another magnificent suite of this species, labelled Gervilii, is to 

 be found in the Museum of Stuttgart. They show the same con- 

 traction of the mouth in large specimens, in some to such an extent 

 that the actual opening is triangular. The only partially constant 

 distinction which I can find between this species and the true Ger- 

 vilii, consists in the smoothness of the young of the latter, their 

 usually smaller size, and the slower increase in magnitude of the 

 whorls by growth. 



Stephanoceras Gervilii. 



Amm. Gervilii Sow., Min. Conch., pi. 184a, fig. 3. 



Amm. Brongniarlii D'Orb., Terr. Jurass., pi. 137. 



The forms of this species are precisely intermediate in point of 

 size, development, and so on, between Brochii and Brongniartii. 

 Some of the specimens in the British Museum have finer ribs than 

 the coarser ribbed Brochii of that collection, but the umbilicus is 



