STUDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 201 



including the skeleton of the dermal and gastral cortex and a 

 normal articulate tubar skeleton; but in addition to these 

 parts we find also a well-developed layer of sagittal triradiates, 

 whose oral rays are extended in the dermal cortex parallel to 

 the surface, while the elongated basal ray projects inwards 

 for some little distance into the chamber layer. The position 

 of these spicules is thus exactly the reverse of that of an 

 ordinary tubar triradiate^ the basal rays pointing in exactly 

 opposite directions in the two cases. 



In Grantessa intusarticulata (4), the anatomy of which 

 is represented in fig. 18^ we find a precisely similar condition, 

 but the chambers are shorter, and the number of joints of the 

 articulate tubar skeleton correspondingly fewer. In this 

 species, also, it is highly interesting to notice that in the 

 youngest portions of the sponge, nearest the osculum, where 

 the chambers are shortest, the skeleton of the chamber layer 

 consists solely of the basal rays of the subdermal and sub- 

 gastral sagittal triradiates, so that we have here a typical 

 example of the so-called " inarticulate '' tubar skeleton. In 

 other words, we find the two types of tubar skeleton, articu- 

 late and inarticulate, existing side by side in the same sponge. 

 In Grantessa poculum, an excellent figure of which, under 

 the name Amphoriscus poculum, is given by Polejaefi* (8), 

 the skeleton is almost exclusively " inarticulate," but I find 

 from my own examination of the sponge that the inner 

 triradiates are not always strictly subgastral, but may be 

 situate some little distance beneath the gastral cortex. 



The dermal and gastral skeleton in this genus agrees so 

 closely with that of Grantia as to require no further com- 

 ment (compare figs. 9 and 18), unless we specially mention the 

 fact that in some species of Grantessa the oxeote spicules of 

 the dermal surface are collected into tufts, which, however 

 bear no relation to the radial chambers. This character, which 

 is well shown in Grantessa sacca, first gave origin to von 

 Lendenfeld^s genus Grantessa (11). I do not believe it one 

 of great systematic value ; and I do not hesitate to include 

 in the same genus species like G. intusarticulata and G. 



