PLATE XCII. 345 



The most satisfactory view of its dermal peculiarities 

 is obtained by tlie examination of a tliin slice from its 

 sm^face witliout immersion in Canada balsam, tlio 

 areas of tlie pores are tten distinctly and beauti- 

 fully apparent surrounded by dense masses of 

 spicula projected from beneatli. The areas rarely have 

 any tension spicula embedded on their surfaces, but 

 they are abundantly furnished with the different forms 

 of retentive spicula. The bihamate spicula are not 

 very numerous and the larger description of bidentate 

 equi-anchorate ones still less so, but the smaller 

 description of the bidentate equi-anchorate ones are 

 frequently abrmdant and especially so round the 

 margins of the open pores, when the same slice from 

 the dermal surface has been immersed in Canada 

 balsam these characters are rendered very much less 

 distinctly as the membrane becomes very translucent. 

 The retentive spicula are important characters in the 

 discrimination of the species, although they are very 

 small, reqiiiring a power of about 700 linear to render 

 them distinctly to the eye. The bihamate ones are of 

 two distinct forms, the largest are mostly contort with 

 slender shafts and acute terminations, an average-sized 

 one measured xaW ™ch in length ; the small descrip- 

 tion of bihamate speculum appears always to be of the 

 simple description, with the hami in the same plane, 

 their shafts are equable in diameter and the terminations 

 of the hami are obtuse ; an average-sized one measured 

 T-ufo i^ch in length. The bidentate equi-anchorate 

 spicula were of two distinct sets, but of the same form. 

 The largest were very few in number, they measured 

 j-aVo iiich in length. The smaller description of the 

 same form were not very numerous, but much more so 

 than the larger ones ; an average-sized one did not 

 exceed g^tro ™ch in length. The skeleton is well 

 developed and the spicula are rather short and stout 

 and well furnished with acutely conical spines, especially 

 towards the bases and apices. Intermixed with this 

 form there are occasionally a few smooth acerate 



