Hyatt.] 394 [June 7, 



quite as open, and it is possible that the young have the same 

 resemblance to the young and adults of contractum, but this could 

 not be ascertained. The young of the typical English and German 

 forms are precisely similar to the full grown Brocchil of the more 

 contractum-like varieties, aud appear never to have tubercles at any 

 age, being remarkably gibbous even at the earliest stages. 



I do not pretend to draw a distinct and definite line on either side 

 of this species, since the indications are numerous that it fades in 

 one direction into true BroccJiii, and in the other into Brongniartii. 

 The latter takes place through the smaller and more involute vari- 

 eties with globular young and finer ribs. In the Palaeontological 

 Collection at Munich there are several species described by Waagen 

 as belonging to Stephanoceras which belong to Gervilii, or some of 

 the forms intermediate between this and the true Brocchii forms, 

 such as Amm. polyscliides and Amm. jjolymerus. Amm. evolvescens 

 appears to be a form of Brongniartii. The species which occur in 

 the Macrocephalus-bed have been named Amm. Bombur Oppel, and 

 it may perhaps be convenient to retain this name, since they seem 

 to be constantly smaller than typical Gervilii, but retain the coarser 

 ribs and more open umbilicus of that species in the young. 



Stephanoceras Brongniartii. 



Amm. Brongniartii Sow., Min. Conch., pi. 184a, fig. 2. 



Amm. Gervilii D'Orb., Terr. Jurass., pi. 140. 



The irregular growth of the living chamber, which resembles so 

 closely that of Scaphites, becomes in this species a fixed character, 

 and is found at an early age, though less marked than in the adults. 

 The young are smooth until a late stage of growth, when compared 

 with those of the preceding species, very globular in form, and the 

 ribs when they begin to appear are very fine and untuberculated. 



I find no mention of this species in my notes on D'Orbigny's col- 

 lection, and doubt if it existed there, since he does not allude to any 

 originals as belonging to his own collection. The lateral expansions 

 figured by him in the early stages are very distinct in position and 

 form from those of the Sauzei group. From the study of several 

 specimens of about the same age, I should think they were very 

 much exaggerated in D'Orbigny's drawing. The edge of the mouth 

 is generally bent inwards, but in some specimens it may be thrown 

 outwards, forming a salient angle, but no wings or lappets were 

 observed in the young. 



