Hyatt.] 234 [December 2, 



near the abdomen did not probably exist in the living shell. The ab- 

 domen also has a decided keel, which is not represented in the plate. 



Oxynotieeras Guibalianum Hyatt. 



Amm. Guibalianus D'Orb., Ter. Jurass., Ceph., p. 259, pi. 73. 



Amm. Guibalii Reynes' Plates (pars). 



Amm. Guibalianus Reynes' Plates (pars). 



The examination of German specimens leads me to the conclusion 

 that this species was closely allied to Oxynotieeras oxynotum in devel- 

 opment and in septa, but the matter still remained doubtful until I 

 reached Semur. Here the splendid suite of specimens of this spe- 

 cies enabled me to solve all difficulties. Here also I was enabled to 

 compare it with specimens of the true Collenotii D'Orb., the originals 

 of which are in the Museum of Comp. Zool. at Cambridge. 



They have not the slightest claims to be considered identical. Op- 

 pel, who has identified many species, was probably led astray by the 

 miscellaneous collection of supposed types in D'Orbigny's Collection. 

 Reynes has divided this species into three forms, not very readily 

 distinguishable by their adult characteristics, but quite distinct when 

 their development and old age are studied. His principal observations 

 on Lotliaringus Guibalii and Guibalianus were made in the Museum 

 at Semur. I, however, am obliged to refer his Guibalii to Guibalianus 

 D'Orb., because of their close resemblance in development and old 

 age, and in order to avoid the use of a new name I distinguish the next 

 species, his Guibalianus, as Guibalii. In this also I am justified by the 

 types in the Semur Collection, in many of which these names are in- 

 terchanged. The true Guibalianus D'Orb., as may be seen by com- 

 parison of the original specimen and the Semur collection, has more 

 abrupt umbilical shoulders, a more open umbilicus, is less involved, 

 and retains the keel and typical form of the whorls until a later stage 

 of growth than any of the group except 0. oxynotum. The shell some- 

 times attains the size of 235 mm. before any marked change of 

 form is observable, and in one specimen reached the size of 410 mm. 

 before the keel disappeared. Finally, however, the keel begins to dis- 

 appear and eventually all traces of it vanish in the almost flattened 

 abdomen. The form, however, seldom changes as completely as in 

 0. Guibalii. The length of the ribs, whether long, or alternately 

 long and short, seems to be a characteristic of great variability, and 

 I have not been able to make it of any use in distinguishing the 

 species. 



