1870.] 41 [Hyatt. 



ANDROGYNOCERAS. 



From the specific descriptions it will be seen that we have here 

 two groups or series, both developing from the first variety of one 

 species, Androgynoceras hybridum. From this we have the series in 

 which acceleration of development produces the flattened abdomens 

 and broad whorls of the second variety of A. hybridum, and of 

 Liparoceras indecisum, the more elevated, though still broad whorled 

 adult of L. Henleyif with young just like the adults of A. hybridum, 

 second variety, and finally the high whorled L. Bechei. The amount 

 of involution is just proportionate to this progress, reaching to the 

 first line of tubercles in the first three forms, to the second only in 

 the adults of the fourth, and to the second in both the young and 

 adults of the fifth. 



The second offshoot or series contains only one species, A. 

 appressum, which is highly accelerated when compared with A. 

 hybridum. This has remarkably flattened sides and the connection 

 with the other is shown by the development of the young. Whether 

 this ought to be set aside as a distinct genus, or not, will depend upon 

 the discovery of other descendants. 



Androgynoceras hybridum. 



Amm. hybrida D'Orb., Terr. Jurass. Ceph., p. 285, pi. 85. 



And. hybridum Hyatt, Bull. Mus. Comp. Zool., no. 5, p. 83. 



For six volutions the shell is apparently inseparable from certain 

 forms of M. laticosta. Upon the seventh whorl, instead of continuing 

 the same degree of increase in size, a more rapid enlargement takes 

 place, the lateral pilas become less prominent and more crowded, 

 sometimes coalescing near the umbilicus. The inner tubercles in the 

 latter case, also, either partially or entirely coalesce. The abdomen 

 in the meantime has become more prominent, less furrowed, and 

 more rounded, and the sides converge outwardly. The abdominal 

 pilse split up each into several minor ridges on the latter part of the 

 seventh whorl, reducing these furrows to a minimum. 



A variety of this species from Schippenstadt and Semur completes 

 the same stages of growth as have been described in A. hybri- 

 dum, a full volution earlier. It has at the end of the sixth volution a 

 whorl nearly as large and of the same form, but much broader in pro- 

 portion to the length than in the first. The pilas begin to take upon 

 themselves similar characteristics. I am unable to state whether this 

 or some intermediate form between this and the first variety is the 



