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•EKDEAVOUE" SCIENTIFIC KKSL LTS. 



undifferentiated auxiliary spicules yet in many of the species 

 which ha\ e been assigned to KhaphidopJiJus (including among 

 theni^ — I have reason to believe — the type-species) the dermal 

 spicules are of a special kind. It would seem therefore that the 

 basis for a distinction between the two genera is to be sought 

 for, not to any extent in the degree of dexelopment of the 

 dermal skeleton, but rather — in what is essentiallv of greater 

 systematic importance — in the nature of the spicules compos- 

 ing it. It is quite probable that this distinction also will be 

 found to break down ; but in the absence of any well estab- 

 lished e\ idence in proof of this, it seems to me not improper 

 to still emplov, tentatively, the name RliaphiilopIiJus for such 

 species as those herein described, \iz., R. typicus, R. pauci- 

 spiuiis, and R. rcticiihihis. 



It cannot be regarded as other than a fact of considerable 

 significance that in R. typicus and in R. paucispinus the con- 

 stitution of the dermal skeleton is precisely the same ; yet the 

 difference in the characters of their microscleres show the two 

 species, considered as members of a single genus, to be rather 

 widely separated. Thus, although in R. typicus the chela? 

 have become differentiated into two groups and the indi\ idual 

 toxa replaced by toxodragmata, whilst in R. paucisphrus 

 neither of these changes has occurred ; yet in both species we 

 find that the dermal skeletoji consists of reticulating lines of 

 upright shorter styli underlain by horizontally disposed longer 

 stvli" This t\pe of dermal skeleton would therefore appear to 

 be phvlogenetically one of long standing, and on that account 

 I0 confer on these and related species^ no slight claim to con- 

 g^eneric distinction. On the other hand, since the vertically 

 disposed or special dermal styli as they may be termed, are 

 (as is evident from a study of the two species referred to) 

 nothing more than a section of the auxiliary spicules which 

 have become slightly modified in correlation with their fulfil- 

 ment of a special function, it follows that species in which the 

 transitional types of dermal skeleton have persisted, may 

 reasonablv be expected to occur. This consideration points to 

 a possible difficulty in the way of satisfactorily defining and so 

 justifving the maintenance of Rhaphidophlus, but it does not, 

 in itself, pr«n ide a sufficient reason why the genus should be 

 rejected. 



Among the species, which must be taken into account m 

 devisin"^ a suitable definition for the genus, is the interesting 



1 Bv "related epecies" I do not imply merely those which possess a 

 Bimilar type of dermal skeleton, but would also include any which mipht 

 a^rd proof of their derivation therefrom, even thouith their special 

 dermal styli had become i^econdarily nonexistent. 



