200 ARTHUR DENDT. 



certainly appears to be a difficulty in the way of utilising the 

 presence of subdermal quadriradiate spicules as a family cha- 

 racteristic in the Araphoriscidse, but in the latter case the apical 

 rays are so constant, and form, in most cases, such an im- 

 portant part of the skeleton, that we must treat the question 

 from a different standpoint. 



Leucyssa. 



In the skeleton of this genus we meet with a parallel case 

 to that of Sycyssa, only associated this time (presumably) 

 with a Leuconoid canal system. 



The genus is very imperfectly known, and what we do know 

 about it we owe chiefly to Haeckel (6). Two of the three 

 species (L. spongilla and L. cretacea) are described from 

 single specimens, and a third (L. incrustans) is extremely 

 rare. In all, the skeleton appears to be quite irregular, con- 

 sisting of a felt-work of oxeote spicules. In L. spongilla the 

 spicules are spindle-shaped, straight, and smooth. In L. 

 cretacea they are swollen at one end and pierced like a 

 sewing-needle ; and it is interesting to note that similar spi- 

 cules are found in Leucandra ochotensis (5). In Leu- 

 cyssa incrustans (Carter^s Trichogypsia villosa), a 

 European species which, thanks to the kindness of Mr. Carter, 

 I have had the opportunity of partially examining (in the dry 

 state), the skeleton consists of a very dense, irregular felt-work 

 of spinose oxea. 



Grantessa (fig. 18). 

 In this genus we have an entirely new element introduced 

 into the composition of the skeleton, in the form of sub- 

 dermal sagittal triradiate spicules. The existence of 

 these spicules in certain species has long been recognised, but 

 their importance from a systematic point of view appears to 

 me to have been under- rated. They never appear, so far as ray 

 experience goes, in sponges without a dermal cortex, and they 

 seem to be first introduced as additions to the ordinary 

 Grantia type of skeleton. Thus in Grantessa sacca (4, 11) 

 we find all the parts of a typical Grantia skeleton present. 



