liv 



THE VOYAGE OF H.M.S. CHALLENGER. 



Bowerbank tliought that he had discovered the great desideratum in the arrangement 

 of the skeleton, and his subfamilies and genera were consequently made to depend solely 

 upon this character. But a glance at his sj^stem shows the utter failure of such an 

 attempt. Let us take an example from his work •} — " Order II. Silicea. Suborder I. 

 Spiculo-radiate skeletons. Not reticulate. Composed of spicula radiating in fasciculi or 

 separately from the base or axis of the sponge." In this suborder Bowerbank places the 

 following genera : — 



1. Geodia (Tetractinellid). 



2. Pachymatisma (Tetractinellid). 



3. Ecionemia (Tetractinellid). 



4. Alcyoncellum (Hexactinellid). 



5. Polymastia (Monaxonid). 



6. Ilalyphysema (Foraminifer). 



7. CiocaJypta (Monaxonid). 



8. Tethea (partly Tetractinellid). 



9. Halicnemia (Monaxonid ?). 



10. Dictyocylindrus (Monaxonid). 



11. Phakellia (Monaxonid). 



12. Microciona (Monaxonid). 



13. Hymeraphia (Monaxonid). 



14. Hymedesmia (Monaxonid). 



Such is the result of applying the arrangement of the skeleton as a sole guide to the 

 distinction of genera ; we need say no more. 



But although the arrangement of the skeleton cannot be applied by itself to the 

 distinction of genera, yet it is by no means valueless as a guide to classification when 

 taken in conjunction with other characters, especially when applied to larger sul)divisions 

 than genera. Thus, in the more careful and discriminating hands of Mr. Carter it has 

 led to much better results ; the Axinellidee, Ectyoninse, and Suberitidse, being all 

 characterised by special types of skeleton arrangement fairly constant within the group ; 

 still it is at the best an uncertain guide. 



Hitherto a great deal of reliance has been placed upon the greater or less amount of 

 spongin, or horny cementing material, present in the skeleton, but of late years this 

 character also has been losing favour amongst spongologists. Indeed, as has already 

 been pointed out, it is the great merit of Dr. Gray's system that in it the horny sponges 

 are included amongst the SUicea. Dr. Gray was, however, a good deal in advance of his 

 times in this respect. AVe hope to show in this place that even within the group of 

 Monaxonida the amount of spongin present varies in such an irregular fashion as to be 

 of comparatively little use for purposes of classification. 



In all the Halichondrina spongin is usually present, and we find that the amount 

 stands, roughly speaking, in inverse proportion to the number of spicules. Thus, taking 

 first the Homorrhaphidse, the division between the Renierinse and Chalininse is a purely 

 arbitrary one ; both groups contain more or less spongin, very few (if any) species even of 

 Renierinse containing none, while in the Chalininse the amount is relatively very large. 



1 Mon. Brit. Spong., vol. i. pp. 159, 167, ka. 



