1876.] 391 [Hyatt. 



without any contraction in the magnitude of the whorls. These are 

 also smooth in the adult. 



The resemblance of the young of the first varieties to coronation, 

 and the mode of growth and subsequent retrograde metamorphosis 

 by a decrease in size, shows that we are dealing with forms derived 

 from the coronatum series, and which, notwithstanding the close resem- 

 blance of the fourth, or modiolare variety, to Amm. Lalandeanus, do 

 not seem to lead into this group. 



FIFTH SERIES. 



Stephanoceras contractum. 



Amm. contractus Sow. (pars.), Min. Conch., pi. 500. 



Under this name I have, for convenience sake, assembled those 

 forms which are intermediate between subcoronatum and the ma- 

 crocephalum, Broccldi and Sauzei series. They are usually recog- 

 nized in collections, either as varieties of 'subcoronatum, as Brocchii, 

 as linguiferum, as Humphriesianum, etc., and also as true contractum. 

 From this they vary, however, in the fineness of the abdominal 

 ribs and the immature aspect of the lateral ribs. This last char- 

 acteristic is so marked that the umbilicus resembles that of Pettos 

 very closely in the smooth, abrupt aspect of the sides, and the 

 prominence of the tubercles. The varieties lead from a very open 

 discoidal whorl in one direction into the true Brocchii form, and in 

 another into the Braikenridgii. 



Stephanoceras Herveyi. 



Amm. Herveyi Sow., Min. Conch., pi. 195. 

 " " Ziet, Verst. Wurtt., pi. 14, f. 3. 



The young of this species varies considerably in aspect. Some 

 specimens have a row of prominent tubercles on the side, closely 

 appressed so as to form an almost continuous ridge. Others have 

 them more scattered, and finally there are many without any, and 

 wholly indistinguishable from the untuberculated young of Brocchii, 

 if found in the same formation. They are invariably stouter, rounder, 

 and less Pettos-like than the young, or even adults of the subcoro- 

 natum-like varieties of the contractum from Dundry, Eng. The pecu- 

 liar abdominal ribs are in the young no coarser than in Brocchii, and 

 it is evidently a lineal descendant of the tuberculated Brocchii-like 

 forms of Steph. contractum. 



