Hyatt.] 390 [June 7, 



FOURTH SERIES. 



Stephanoceras subleve. 



Amm. sublevis Sow., Min. Conch., pi. 54. 



Amm. modiolaris D'Orb., Terr. Juras., pi. 170. 



Amm. sublevis Quenst., Die Ceph., pi. 14, f. 6. 



Amm. sublevis Zieten, Verst. Wurtt., pi. 28, fig. 5. 



The originals in Sowerby's collection prove the accuracy of 

 Quenstedt's conclusions with regard to the identity of the English, 

 French and German forms. D'Orbigny's collection possesses only a 

 cast, but his figures are quite sufficient. 



Amm. sublevis Zieten, which Quenstedt identifies with modiolaris, 

 is represented by several specimens in the Upper Brown Jura, Ma- 

 chrochilus-bed, Museum of Stuttgart. One of these is much thinner 

 than the others, and shows a more discoidal young. The rest have 

 very abrupt sides from an early period, and deep umbilicus, but not 

 so deep as in D'Orbigny's figure. These show that the form is not 

 developed as in Quenstedioceras Leachii, and others of the Goliathus 

 group, to which the adult of the modiolare variety seems to be 

 closely allied, but according to the method commonly observed in 

 the coronatum group. 



A very fine suite of this species exists in Quenstedt's collection, 

 from which I obtained the following observations. One variety retains 

 until a late stage of growth a very close resemblance in form and 

 characteristics to the coronatum as figured by D'Orbigny, and which 

 has been cited from the Parkinsoni-bed in the collection of the Mu- 

 seum of Stuttgart. Whether the whorl ever becomes entirely smooth 

 in this variety I cannot say; they attain a considerable size without 

 any marks of such a retrograde metamorphosis. The umbilicus is quite 

 open, and the young in form and characteristics approximate to the 

 adult of coronatum. A second variety may be distinguished, which is 

 a true subleve form, but still has quite an open umbilicus. This 

 loses its ribs and becomes smooth at a late period of growth on the 

 abdomen, but retains heavy lateral ribs. A third variety has an 

 open umbilicus, but is comparatively smooth at an early age, losing 

 the lateral as well as the abdominal pilae, and finally the whorl begins 

 to show a retrograde metamorphosis, the size being affected by con- 

 traction, as in large specimens of Steph. Gervilii or Steph. Humphrie- 

 sianum. A fourth variety has the narrow funnel-shaped umbilici, and 

 the individuals appear to continue to increase in size throughout life 



