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vise a simple method of arranging the various species, based on this 

 character. By comparing the different forms, w^hich vary from nar- 

 row tapered blades to those having a conspicuous fin-like base, they 

 are found to grade into one another, and fall into the following natural 

 divisions or groups, to which apparently Saint -Joseph's names can be 

 applied : 



A. In the forms having the distinct fin-like base, the fin angular or 

 rounded, there are apparent differences in the serrations, which are 

 separable into two groups. In the first the serrations on the edge of 

 the blade are comparatively fine and the spines on the fin usually much 

 coarser (p1. xl, fig. 12) . Taking Spirorbis borealis Daudin, now con- 

 sidered synonymous with 6". spirorbis Linne, as the type species, there 

 should be a few (3 to 5) odd setae with elongated fringed ends in the 

 third fascicle of thoracic setas. This is Spirorbis in its strictest sense. 



B. In the second form the serrations become very coarse on both the 

 blade and fin (pi. xxxvii, fig. 24) . As militaris Claparede falls into 

 this group, it is equal to the genus Pileolaria Claparede + Saint- 

 Joseph, which, according to the latter, has no odd setae. 



C. The form with rounded fin gives rise to those in which the fin is 

 defined only by a more or less definite notch, which entirely disappears, 

 forming simple tapered blades (p1. xli, fig. 3). In this group are 

 both pagenstecheri Quatrefages, referred to Janua by Saint- Joseph 

 as type, and pusillus Saint-Joseph, referred to Mera as type. The first 

 is described as having the odd setas of Apomatus on one or more 

 segments, while the second has them on the third only, so that there 

 seems to be no distinguishable difference between them, except in the 

 form of the operculum. Mera therefore becomes synonymous with 

 Janua ^ the name of this third group. 



D. The form with angular fin gives rise to a simple blade, broadly 

 angular at base, found in armoricanus Saint-Joseph, referred to 

 Circeis as type (p1. xli, figs. 1,2). 



E. Instead of being angular, the blade becomes broadly rounded at 

 base, as in Icevis Quatrefages, referred by Saint- Joseph to Leodora as 

 type. Caullery and Mesnil suggested the possibility of this proving 

 synonymous with the following group. 



F. The blades become long, narrow, regularly tapered, and similar 

 in all three fascicles, as in perrieri Caullery and Mesnil, the type of 

 Romanchella Caullery and Mesnil (p1. xxxvii, fig. 8). 



None of these groups or divisions are sufficiently disconnected or 

 distinct to give them generic (after Saint- Joseph) or subgeneric (after 

 Caullery and Mesnil) value. B"t since the names have been proposed, 



