﻿176 ■KXJJEAVOrK" SCIENTIFIC UKSl LTS. 



undifferentiated auxiliary spicules yet in many of the species 

 which ha\ e been assigned to Rhaphidophlus (including among 

 them — 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 development 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 

 lound 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 employ, tentatively, the name Rhaphidophlus for such 

 species as those herein described, viz., K. typicus, R. paiici- 

 spitius, and R. rcliciihiliis. 



It cannot be regarded as t)ther 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 individual 

 toxa replaced by toxodragmata, whilst in R. paucispinus 

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

 Hnd that the dermal skeleton consists of reticulating lines of 

 upright shorter styli underlain by horizontally disposed longer 

 styli. This type of dermal skeleton would therefore appear to 

 be phylogenetically one of long standing, and on that account 

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

 generic distinction. On the other hand, since the vertically 

 disposed or special dermal styli as the}' may be termed, are 

 (as is e\ ident from a study of the two species referred to) 

 nothing more than a section of the auxiliary spicules which 

 have become slightlx' modified in correlation with their fulfil- 

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

 transitional tvpes 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 

 justifying the maintenance of Rhaphidophlus, but it does not, 

 in itself, prox ide a sufficient reason \\h\ the genus should be 

 rejected. 



Among the species, which must be taken into account in 

 dex'ising a suitable definition for the genus, is the interesting 



1 By "related species" I do not imply merely those which possess a 

 pimirar type of dermal skeleton, hut would also include any which mipht 

 afford proof of their derivation therefrom, even thougrh their special 

 dermal stvli had heeome secondarily non-existent. 



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