Hyatt.] 230 [December 2, 



development last described. There are two specimens in the Geo- 

 metricus bed (Stuttgart Museum), but they do not show the young 

 or give any better clue to the true development. There are three 

 casts in the Stuttgart Museum from the Pentacrinus bed near Krumen- 

 acher, which appear to be the 'young of this same species, and one of 

 them with the shell on shows all the peculiar marks of Agassiceras 

 striaries, while another is so broad, on the abdomen, and the broad, 

 fold-like pilse are so high, that it looks remotely like the young of Cor. 

 Sauzeanum. The three are identified as young of Coroniceras Sauze- 

 anum, but the young of this species is very distinct in septa and all 

 its characteristics. In the Collection at Semur is a specimen which, 

 until a late period of its growth, maintains the aspect of striaries and 

 then develops the keel and perfect form of Scipionianus. The Scip- 

 ionis of Reynes is a form which at an early age becomes smooth like 

 the old stage of Scipionianus. 



Family OXYNOTIDJE. 



I have thought it essential here to designate the group below as 

 distinct from the Arietidse because of its great difference in develop- 

 ment, in adult characteristics, and especially in old age. The young 

 are similar to the group of certain aberrant forms of that family, as 

 noticed below, but the adult, instead of the solid keel of the Arie- 

 tidse, possesses a hollow keel. In the old, however, this keel entirely 

 disappears, leaving the abdomen rounded and almost flattened, a 

 transformation entirely distinct from that which occurs in the old of 

 any of the Arietidoe. Here, as elsewhere, however, a single charac- 

 teristic unites the two ; the sutures are similar in both families. 

 The similarities of the young are such as occur commonly between 

 what are supposed to be very widely separated adults in many other 

 distinct families or groups. 



OXYNOTICERAS. 



This group, which has heretofore not been treated of in a con- 

 nected form, so far as I know, is perhaps one of the most interest- 

 ing. Baron Schwartz, to whom I am indebted for being made aware 

 of the importance of the hollow character of the keel among the 

 Ammonites, was, at the time of my visit at Tubingen, searching for 

 specimens of O. oxynolum in which the structure of the keel could be 

 studied. It was my good fortune to find several specimens in the 

 collections at Stuttgart and Semur which showed the essentially hoi- 



