1876.] 385 [Hyatt- 



FIRST SERIES. 



Stephanoceras Bayleanum. 



Amm. Bayleanus Oppel, Die Juraf., p. 497. 



Amm. Humphriesianus D'Orb. (pars), Terr. Jurass., pi. 133. 



Oppel did not find the intermediate forms between this species 

 and Humphriesianum, and therefore considered it distinct. Although 

 this view is untenable, I retain the specific name in accordance with 

 previous custom, otherwise I should be obliged to use a trinomial 

 designation for this form, and others of the same group. The tran- 

 sition forms from this to the next described, are numerous, and can 

 be observed in any large collection. The young were not observed. 

 According to Oppel, it is found lower than Humphriesianum in 

 Germany. 



Stephanoceras nodosum. 



Var. Humphriesianus nodosus Quenst., Der Jura, pi. 54, f. 4. 



Amm. Humphriesianus Sow., Min. Conch., pi. 500, fig. 3 (not 1-2). 



The typical form of this variety has more prominent tubercles and 

 fewer lateral ribs than the typical variety of Humphriesianum. The 

 young also resemble the adults of Blagdeni until a later period of 

 growth than in the last mentioned. All these characteristics are 

 subject to great variation, and both by the adult characteristics and 

 development these forms fade into the next described. It occurs in 

 the Mus. Stuttgart Coll., associated with Sauzei in the Middle Brown 

 Jura y. The originals in Sowerby's collection show that the large 

 specimen figured on pi. 500, fig. 3, of his Min. Conch., must be in- 

 cluded in this variety, while figs. 1 and 2 must be referred, as they 

 have been, to subcoronatum. 



Stephanoceras Humphriesianum. 



Amm. Humphriesianus Auct. 



Var. Humphriesianus plicatus Quenst., Der Jura, p. 398. 



Amm. Humphriesianus D'Orb., Terr. Jurass., pi. 134-135. 



The typical forms are found in the Middle Brown Jura and in the 

 Mus. Stutt. Coll., with the first of the true eoronatum forms. The 

 varieties appear to have two principal tendencies, one which leads 

 into forms similar to Humphriesianus plicalissimus Quenst., and occurs 

 in the upper part of the same formation (oberer Delta), and one which 

 approximates to the Amm. subcoronatus Oppel. One fine specimen of 

 this form showed an incomplete living chamber at the diameter of 

 156 mm., about half a volution in length. This was smaller in 



PROCEEDINGS B. S. N. H. — VOL. XVIII. 25 DECEMBER, 1876. 



