86 RECORDS 



oped by total cleavage into a perfect larva of dwarf size. It 

 thus appears that localization is progressive, being practically 

 absent before the initial cleavage, appearing in the two-cell 

 stage, and becoming greater in the different regions of the blas- 

 tula. The relation between cell-division and differentiation was 

 discussed. It is expected that this paper will be published in 

 full at an early date. 



Professor Grabau showed that the Fusidse are among the 

 more highly accelerated types of marine gasteropods of the 

 modern fauna. Fiistis itself dates back to the Eocene, oc- 

 curring in the Paris and Hampshire basins. The American 

 Eocene species generally referred to Fjishs are shown by their 

 protoconchs to be more nearly related to Plenrotoma although 

 their adult form is like that of the typical Fusus. The proto- 

 conch of Fusus is highly accelerated, showing riblets on the last 

 portion. The typical conch ornamentation appears abruptly. 

 The earliest stage is characterized by round whorls, rounded 

 ribs extending from suture to suture, and simple spirals. These 

 are the characters of the adult of the most primitive Eocene 

 species, and also appear in the young of all later species. The 

 next stage is characterized by the appearance of an angulation 

 on the whorl, and a concentration of the ribs on the angle. In 

 the next stage the ribs are replaced by tubercles, and these later 

 unite to form a keel. This gives the type of the genus Fusus 

 coins. In the old members of this species the keel is lost, and 

 the whorls become rounded. Finally in highly accelerated 

 types the adult is marked by the rounded keelless whorl, while 

 many of the intermediate stages are dropped out. Thus F. lon- 

 gicauda has dropped the tubercled and keeled stage through a 

 process of acceleration in development. This may be consid- 

 ered as phylogerontism. In every genetic series of the Fusidse 

 types occur, which in their adult conditions, show characters 

 comparable to one or the other of the stages found in such 

 types as F. coins. In the chronogenesis of each series it is 

 found that types whose adults are comparable with the earliest 

 stage of F. coins appear first. All Eocene species of Fusus for 

 example are of the simplest type. The more complicated 



