76 TRANSACTIONS OF THE WAGNER FREE 



As the era of Voliitilitlies , especially the Eocene part of it, was one when 

 the group was, so to speak, pregnant with evolutionary possibilities, it is as 

 well not to attempt a fine-drawn separation of its species into sections. In 

 order to point out the lines of variation, then hardly more than specific, but 

 which have since become differential of genera and subgenera, I will here in- 

 dicate the suggestions which have resulted from a study of the material here- 

 inbefore referred to. 



In the Cretaceous period, I believe the modifications of the intracapsular 

 development had already been initiated. The small shelly, trochoid nucleus, 

 which had been inherited from the fusiform ancestry of the group, of course 

 existed, as we have shown ; the large Cymba nucleus, which in recent species 

 is associated with the development of single individuals in the matrix of the 

 parent and not in a capsule deposited on some foreign object, had already been 

 developed. The steps between these are wanting at present, owing to the im- 

 perfection of the geological record. But I regard Rostellites and Volutoinorpha 

 as probably representing the ancestry of the true Vobitilithes in our American 

 rocks, and Volutocorbis and Vohitilitlies as the Eocene examples of analogous 

 surface-structure. 



In the Eocene, however, the links between the different branches of this 

 stock appear to be pretty well indicated. A large series of any one species 

 will show occasional instances of variation in the nucleus to vary from the 

 normal type. It tends to become bigger, more irregular and swollen. The 

 gap between Vohitilithes and Valuta is not wide. An enlargement of the 

 shelly nucleus, a tendency of the sculpture to become more rounded, less 

 spinose and less sharp; and for the ribs to become emphasized rather than 

 the spirals ; the failure of the internal lirse on the outer lip and an increase of 

 them on the inner lip (changes probably connected with a widening of the 

 adductor attachment on the pillar), and the change was accomplished (see PI. 

 6, figs. 1,2). A careful study of a series of the specimens shows how very 

 slight the modification really is. 



The recent Vobitilithes Philippiana has no operculum, but, being a deep- 

 water shell, this might be a recent modification. I think all the Eocene Vo- 

 /?/^zd'^ probably had opercula. The dentition of the recent Volutilithes \s, zs 

 one might expect, rather generalized in form. It has the wide, rather straight 

 rhachidian base of Vohita, but only the three simple cusps o'i Lyria. We can 

 separate the typical Vohita (iimsica L.) from Lyria by its dentition and its 

 larger and more sculptured nucleus. Vohita thus typified would seem to be 

 modern and not to be definitely traced back of the Pliocene, as far as we now 

 know. The Eocene species of this type would better all be referred to Lyria, 

 of which Otockeihis Conrad is a synonym. I find the prototype of Vohita mtisica 

 in the Miocene Lyria inississippicnsis Conrad, which is identical with the older 

 Lyria costata Sowerby. But the type appeared earlier in Europe, as is 



