1876.] 395 [Hyatt. 



SEVENTH SERIES. 



Stephanoceras mierostomum. 



Amm. microstomas D'Orb., Terr. Jurass., pi. 142, fig. 3-4. 



This is a constant and well marked variety, which differs in the 

 young from Steph. platystomum. Many specimens at an advanced age 

 do not become smooth on the living chamber, but others do at a 

 comparatively early stage. It never attains the large size or stout 

 whorls of platystomum, and the living chamber becomes remarkably 

 flattened laterally. The living chamber is almost entirely absorbed 

 at each renewal of the shell growth. 



I find in my notes no mention of any specimen exhibiting the 

 abdominal lappets figured by D'Orbigny, and a strict examination, 

 including the cleaning of several fine specimens, of D'Orbigny's col- 

 lection, was equally fruitless. Quenstedt also could not find them on 

 the German specimens, and I am therefore forced to the conclusion 

 that D'Orbigny's figure is erroneous in this respect. Several of 

 these specimens had perfect mouth outlines. An examination of the 

 young led me first to suspect that these lappets did not exist, and 

 that the species must belong to the entire mouth series, and I could 

 not understand their appearance in a form so evidently closely re- 

 lated to platystomum. A very remarkable series exists in Prof. 

 Mcesch's collection at Zurich. It is the Amm. Ymir Oppel, Amm. 

 bullatus Kudernatsch, a variety intermediate between Gervilii and 

 this species, and found in the Parkinsoni-bed. The living chamber 

 in one specimen is more than one volution in length, smooth for a 

 half of its length, and not yet complete. 



EIGHTH SERIES. 



Stephanoceras platystomum. 



Naut. platysiomus Rein., Naut. et Argo., fig. 3. 



Amm. platystomus Quenst., Die Ceph., pi. 15, f. 3. 



Amm. bullatus D'Orb., Terr. Jurass., pi. 142, f. 1-2. 



This species is most admirably described by Quenstedt, and the 

 affinities traced to the coarse ribbed varieties of his Brongniartii, 

 which are identical here with Gervilii. I have only to add that I 

 have verified his conclusions in several collections, but notably in 

 the Stuttgart and British Museum collections. The resemblance 

 which he describes between the form at certain stages and the Amm. 

 Goliathus D'Orb., is certainly quite remarkable, but a close examina- 



