PHYLOCENY OF FUSUS AND ITS ALLIES. 5 



In extremely accelerated or specialized types, such as ClavUithcs and 

 Cyrtulns, the posterior canal is so strong and broad that instead of the 

 simple revolving subsutural band, which marks its existence in the 

 whorls of more primitive species, a broad and pronounced sutural shelf 

 appears. In certain gastropods, though rarely, if ever, in Fnsus, the 

 posterior canal becomes separated from the body- whorl, which re- 

 sults in the formation of a pronounced sutural canal like that of 

 Sycotypus canalimlatus and other species. 



The long anterior canal of the Fusidae which is the continuation 

 of the aperture into the spindle and the columellar portion of the 

 spindle are usually of a fairly constant type in this group, the modifi- 

 cations being mainly in the length and the relative slenderness as well 

 as in the straightness of this portion of the shell. Spirals of several 

 cycles are almost always found on the spindle. In some phylogerontic 

 types, and in certain old-age individuals, the inner lip becomes separated 

 from the columella of the spindle and a slit-like umbilication is 

 produced. 



The Fusidas as a group are highly accelerated, and near the acme 

 of development. Primitive types are uncommon, except in the Eocene, 

 and even there regressive species appear. The majority of species 

 have attained the acme of development for the group, many of them 

 reaching it while still young. This group is therefore uncommonly 

 well supplied with phylogerontic types, and there is scarcely a specific 

 or varietal series which does not have its degraded forms. Fiisiis 

 coins, the type of the genus, is itself a regressively accelerated type, in 

 which the characteristic acmatic features have nearly disappeared in 

 the adult. Excessive degradational acceleration is seen in Cyrtulns, 

 Clarilithcs and similar genera. 



In the present paper, the following genera of Fusoid shells are 

 described : Fnsus, Aptyxis, Falsifusus, Fnlgurofnsns, Hcilprinia, 

 Enthnofnsns, Cyrtulns, Clavellofusus, Clavilithes, Rhopalithcs, and 

 Cosmolithes. I have studied all available species of these genera and 

 I believe that with few exceptions they have been referred to their 

 approximate positions in their respective phyletic series. Of the 

 above genera, Fnsus and Clavilithes are the only ones generally recog- 

 nized, the species of the others being referred to one or the other of 

 these two, or to Fasciolaria. Cyrtulns and Aptyxis have been re- 

 stored to their original generic rank. Euthriofusns has recently been 

 proposed by Cossman for Fnsus hurdigalcnsis. The other genera are 

 new. Of the numerous species generally referred to Fnsus, consider- 

 ably less than one third actually belong to that genus, and most of 

 these are described below. Other species, of which good illustrations 

 have been published, are also noted, while a number of other species 

 not here included, will on close study undoubtedly prove congeneric 



