B. W. PRIEST ON AN UNDESCRIBED SPECIES OF SPONGE. 303 



smaller the -^^q of an inch. There are also a great many bi- 

 hamate spicules, measuring the -gj-g- of an inch. Scattered through- 

 out the interior of the Sponge are a number of fasciculi of fine hair- 

 like spicules, each spicule measuring about the ji-g- of an inch, and 

 having just the same appearance as the raphides in plants. 



A vertical section of the Sponge shows the position of the walls 

 to the outer crust, and, as you will observe in Fig. 4, which was 

 drawn from the section itself, it has the appearance of arches where 

 the cavities are filled with the sarcode. Fig. 1 shows the Sponge 

 much enlarged, before being mutilated for examination, having five 

 of the fistulse on the side exposed to view, and about three more on 

 the other, the tip of one being observed showing over the top of the 

 Sponge. In Fig. 2 we have an enlarged view of one of the fistulas, 

 with a portion of the network (Fig. 3) still further magnified, show- 

 ing the relative positions of the spicules. 



It reminds one rather of Euplectella on a small scale. Dr. 

 Bowerbank noticed the same resemblance, and was led to consider 

 that the genus must be closely allied to Alcyoncellum from that 

 cause, though it is certainly not like it, to my mind, when 

 thoroughly examined, as the spicules of Polymastia do not anasto- 

 matose as they do in Euplectella, besides wanting the flesh spicules 

 of that group.* 



Some of the species of Polymastia have only one fistula, as in 

 P. hulbosa ; in others they are very numerous, as in P. rohusta, but 

 our present species seems to be moderate in its number. The 

 various species that I have come across have the skeleton spicules 

 either acerate, fusiform-acerate, spinulate, or fusiform-spinulate, and 

 in one case bi-spinulate, but none have bi-clavate fusiform spicules, 

 or equi-tridentate anchorate or other anchorate, or bi-hamate 

 spicules, both of which, as we have seen, are present in the Sponge 

 I am describing. I propose, therefore, to name it 



Polymastia biclavata {B. W. Priest). 



Sponge massive, bulbous ; fistulse moderate in number ; oscula 

 at distal extremity ; pores inconspicuous ; dermal membrane pel- 

 lucid, thin, with minute bi-clavate spicules dispersed over its surface ; 

 skeleton spicules bi-clavate fusiform, with abnormal forms of the 

 same occurring occasionally through the Sponge ; interstitial 



* Since writing the above I find that Dr. Bowerbank mentions the same 

 fact in one of his later volumes. 



