148 THE VOYAGE OF H.M.S. CHALLENGER. 



witli very short principals, and comparatively strong and long divergent terminals, whicli 

 vary in number from two to four, though they are generally three (PI. LVII. fig. 8). 

 By the extreme shortening of the princijjals, these terminal rays are often drawn so near 

 to the centra] node, which is usually thickened in such cases, that the whole spicule 

 appears as a many-rayed star round the central node. Were there not countless 

 transitional forms of hexasters wdth six distinct principals, leading up to the many-rayed 

 stellate form, there might be real doubt as to the nature of the latter. As it is, however, 

 the stars can be without difficulty traced back to the triaxial type. I observed the 

 isolated occurrence of discohexasters with short principal rays, and with a varying 

 number of long terminals. As figured on PI. LVII. figs. 9, 10, 11, their resemblance to 

 similar structures in Acanthasciis grossularia is evident. 



As to the dermal skeleton, I have observed some smooth hypodermal oxypentacts of 

 medium size, and numerous smaller dermal pentacts, with straight, rough rays which are 

 conically pointed at their extremities, or else rounded ofi" and even truncated. In the 

 latter form there is an almost constant occurrence of a small boss or elevation repre- 

 senting the undeveloped sixth distal ray. On the other hand, I have never observed any 

 cruciate tetracts. On the inner gastral surface numerous hexacts occur, with straight, 

 rough rays, similar to the above-described dermal pentacts. 



The marked resemblance in form, structure, and skeleton between the basal portion of 

 this form, and the corresponding part of Acanthascus grossulaiia, seems to justify the 

 assumption that the upper portions must also have been like one another. We would 

 therefore expect the presence of oblique projecting pleural oxydiacts and a simple oscular 



margin. 



3. Acanthascus cactus, n. sp. (PI. LVII. figs. 1-7). 



Among the dried specimens of Japanese sponges which Dr. Doderlein brought with 

 him from Enosima, there was a pear-shaped, somewhat laterally compressed, thick- 

 walled form, figured in PI. LVII. fig. 1. This Hexactinellid resembles a sack or beaker 

 in form, is 9 cm. long by 5 cm. broad, and 4 cm. thick. By its narrower end directly, 

 and also by means of several l)asal projections, 3 to 4 mm. in diameter, the sponge is 

 attached to a firm substratum. The superior aperture of the simple gastral cavity, 

 which is about 3 cm. in width, is surrounded by a somewhat sharp-edged smooth margin. 

 On the lower end also, between the basal attaching protrusions, there is an irregularly 

 contoured aperture about 8 mm. in diameter, but possibly the result of subsequent 

 damage. 



The external surface of the body is beset with conical elevations varying in height 

 up to 8 mm. They are largest in the middle of the sponge, and decrease in height 

 towards the oscular margin. They occur at intervals of 1 to 2 cm., and bear on their 



