286 Dr. J. E, Gray on the Arrangement of Sponges. 



2. Dysideidae. 



Sponges massive or dendroidal, formed of fibres constituting 

 a more or less thick coat to the more or less abundant sand or 

 fragments of spicules contained in their centre. 



Dysidea Bm^Halispongia^ Bowerbank, Proc. Zool. Soc. 1872, 

 t. vi. 



The Xenospongiadae are peculiar for having a series of very 

 slender diverging filiform spicules on the circumference, and 

 pencils of similar spicules on the mouth of the oscules on the 

 upper surface of the disk, which appear very different from 

 the spicules of other sponges both in structure and position ; 

 and I am not aware that they have been observed in Dysideidse. 

 Some of the calcareous sponges have the oscule similarly 

 fringed or bearded. 



Order II. Thalassospongia. 



This is a very large and numerous group of sponges, cha- 

 racterized by their secreting the siliceous spicules by which 

 their body is almost universally strengthened ; but the number 

 and form of the spicules very greatly vary in the different 

 kinds. In some, as in the coral-sponges, the body is almost 

 entirely formed of spicules which are united together by a 

 deposit of siliceous matter on their surface, forming the whole 

 into a hard siliceous coralloid body ; in others the sponges 

 merely form a horny skeleton, containing one or more series 

 of spicules in its central line. I am inclined to place the 

 genus Spojigia, which is formed entirely of a horny skeleton 

 without any spicules, as an aberrant or abnormal form of this 

 order, though perhaps we may find, when the habit and 

 structure of these bodies are more known, that some species of 

 true sponges {Spongm) are aberrant sand-sponges which do 

 not collect sand, and other species are aberrant spicular sponges 

 that do not secrete spicules. 



The Thalassospongia may be divided into various suborders 

 according to the spicules which they secrete, and whether they 

 secrete spicules of all, of one, or of two or more of the types 

 of spicules which I described in the 'Ann. & Mag. Nat. Hist.' 

 1873, xii. p. 203. 



The sponges are all provided with more or less abundant 

 simple subcylindrical spicules, which may be regarded as the 

 basis of their skeleton ; but some have spicules of one or more 

 of the other types added to them ; and I am inclined to divide 

 them into suborders according to the various types of spicules 

 by which their body is strengthened ; and they often have free 



