262 A MONOGRAPH OF THE 



fimdibuliformis, Bowerbank, and leaning against a young 

 specimen of Dictyocylindrus, Bowerbank. It is in a very 

 imperfect condition, and does not exceed half an inch in 

 diameter. It belongs to the museum of Natural History at 

 Plymouth. In its structure, it is very closely allied to 

 Halichondria Dickiei of this work ; but so far "as we can 

 judge by the specimen under consideration, it does not ap- 

 pear to be a coating sponge. In structural character, with- 

 out a careful examination, itis very difficult to discriminate be- 

 tween them. The skeleton spicula in both species are acuate 

 and entirely spined, but those of Hal. Dickiei are the more 

 slender of the two in their proportions. The most striking 

 specific difference exists in the tension spicula, which never 

 present the sub-clavate or hastate terminations, which are 

 so characteristic in those of the last-named sponge. Nor do 

 we find the decided mucronation of both terminations as in 

 those of Hal. incrustans. The tension spicula vary to some 

 extent in their form ; occasionally, the base exhibits a slight 

 inclination to mucronation, and sometimes the apex is so 

 obtuse as to almost give the spiculum the character of the 

 cylindrical form ; but the prevailing shape is that of a rather 

 obtusely terminated acuate spiculum. 



The retentive spicula, like those of Hal. Dickiei, are ex- 

 ceedingly numerous on the inner surface of the dermal 

 membrane, as well as on the interstial ones ; and the larger 

 and smaller series are indiscriminately crowded together. 

 No simple or contort bihamate spicula could be detected. 



I have dedicated this species to my friend Mr. S pence 

 Bate, who has laboured so long and so efficiently in the 

 cause of Marine Natural History, and to whom I am in- 

 debted for my first acquaintance with this sponge. 



23. Halichondria granulata, Bowerbank. 



Sponge. Massive, sessile. Surface somewhat rugged. 

 Oscula simple ; small, numerous, dispersed. Pores in- 

 conspicuous. Dermal membrane simple, pellucid ; 

 furnished with sub-inucronate-cylindrical spicula, and 



