Hyatt.] 392 [June 7, 



Stephanoceras macrocephalum. 



Amm. macrocephalus Schlot., Die Pet., p. 70. 



" " Ziet., Verst. Wurt.t, pi. 5, fig. 1. 



No line can be drawn between this species and Herveyi, which 

 has not many exceptions, but as a rule the forms of Steph. macro- 

 cephalum may be distinguished by the flatness of the sides and the 

 more elevated abdomen. The young also take on this peculiar form 

 at an early age. Their earlier stages are precisely similar to those 

 of the untuberculated young of certain varieties of Herveyi. 



The smoothness of the latter part of the living chamber is very 

 perceptible in large specimens of Herveyi and of this form, but not 

 in small specimens, though I have seen many small specimens with 

 nearly complete living chambers. This shows that it is an old age 

 characteristic. 



SIXTH SERIES. 



Stephanoceras Brocchii. 



Amm. Brocchii Sow., Min. Conch., pi. 202. 



This is a convenient designation for a number of forms which in the 

 young are undistinguishable from the Brocchii-like forms of contrac- 

 tum, or rather fade into them. They lose the tubercles of con- 

 tractum at an early period in their growth, and the form grows 

 stouter and more involute, disguising in the adult the resemblance 

 of the young to contractum. Series, however, exist, exhibiting all 

 the stages between them, in the British and Bristol Museums, and 

 a partial one in this Museum. The adults differ from Brongniartii 

 so slightly that it is equally difficult to decide on that side, but 

 some forms have a peculiarity of the growth which shows considera- 

 ble distinctness. They continue to grow or increase in size regularly 

 throughout the entire length of the living chamber during the adult 

 period. A specimen in the Museum of Stuttgart, having the coarse 

 ribs and open umbilicus of the forms which approximate most closely 

 to the true contractum, has a nearly complete living chamber, but 

 shows no signs of becoming smooth or contracting the aperture. 

 Either it must have had a much longer living chamber than is usual 

 in Brongniartii, or possessed these distinguishing characteristics. 

 The true Brocchii forms are therefore simply larger and more invo- 

 lute varieties of contractum, and in extremely large old specimens 

 when the whorl permanently contracts the shell, they become in- 



