66 TRANSACTIONS OF THE WAGNER FREE 



There are at least three well-defined types of Volute larvae among the 

 species of the Parisian Eocene, and when we regard the extreme subdivision of 

 the fossils of f^his area into nominal species practiced by Deshayes, and ad- 

 mirably illustrated, it seems extraordinary that such peculiar and remarkable 

 characters as the larval shells offer should have received from him so little 

 consideration. 



We may classify the larval shells broadly into two groups, those which 

 were shelly from the beginning and those which have succeeded to a horny 

 or uncalcified protoconch which is lost before the larval shell escapes from its 

 ovicapsule. 



In general, the advance in biologic rank of any group in process of evolution 

 is marked, if by any change in the larval conditions, by a decrease in the num- 

 ber of embryos and an increase in size of the individual larvae. In Purpura 

 and Bucciniim it has been shown that a diminution of the total number is 

 caused by the cannibalism of certain inmates of the same capsule which devour 

 their mates, consequently through this extra diet becoming larger and more 

 sturdy than the embryos less unscrupulous, but which may also chance to 

 survive. At all events, great disparity may be observed in the size and devel- 

 opment of larval specimens contained in a single capsule and ready to emerge, 

 not only in the above-mentioned genera, but more markedly in Chrysodornus 

 and Volutopsis, both of which are related to the Volutida, the latter having 

 ovicapsules identical in form and construction with those of Scapliella inagel- 

 lanica and Volutilithes Philippiana ; though the last mentioned are much 

 smaller. 



The latter part of the Mesozoic time for the Volutidce seems to have been a 

 sort of springtime, when important changes were inaugurated, new characters 

 initiated, new lines of development begun, while the particular species varied 

 as if in a state of flux. By the end of the Eocene the group seems to have 

 recovered its equilibrium, less fortunate experiments having fallen by the way- 

 side and the well-defined groups, recognizable in recent fauna and in the later 

 Tertiaries, being pretty well established. 



When the Volutida first begin to appear and branch off from Fusus, Fas- 

 ciolaria and Turbinella the nucleus or larval shell in all these forms was small 

 and shelly, as already stated. 



I have identified this form of nucleus in Volutodernia (or Rostellites), Liopep- 

 lum and Volutilithes. In the latter it is generally well preserved and can be ob- 

 served by anybody. The other forms are generally so imperfectly preserved as 

 to make it a rare occurrence for the nucleus to be found uninjured. 



There are several forms of the shelly nucleus. It undoubtedly preceded 

 the horny one in this group. The original and most common type I may call 

 the trochiforut nucleus (See PI. 6, fig. 3). Externally its spire appears conical 

 or trochoid, polished, unsculptured, and of few whorls. This is the case in 

 Liopeplum and the earlier types of Volutilithes, as well as the Fusoid forms 



