PLATE LXXXII. 267 



tlioir surfaces are profusely funiished witli spicula, 

 especially with tlie loug slender subclavate fusiformi- 

 acuate tension spicula, wMcli in some parts are so 

 numerous and so closely felted together as to nearly 

 render the membrane opaque and to totally obscure the 

 more delicately formed retentive spicula. The skeleton 

 fibre is strongly and compactly produced. The spicula of 

 ■which it is composed might at the first glance be mis- 

 taken for those of Desmacidon constricius ; there is an 

 approximation to the constricted form of their cases 

 like the skeleton spicula of that species, but the con- 

 striction is productive rather of a slight clavation of 

 the base than of the elongated constriction so remark- 

 able in the spicula in D. eonstrictiis. There is another 

 character that serves at once to discriminate the two 

 species, and that is, that the spicula of D. cojnosa are 

 very nearly of the same diameter, but not more than 

 half the length of those of D. constrictus. The sub- 

 clavate, fusiformi-acuate tension spicula of the inter- 

 stitial membranes are as long as those of the skeleton, 

 but not more than one fifth or one sixth of their 

 diameter. The bihamate retentive spicula are largo 

 and stout, and occasionally we find a well-produced 

 symmetrical inflation at the middle of the shaft ; they 

 are exceedingly numerous in both the dermal and inter- 

 stitial membranes. The inequi-dentato-palmate ones 

 are very few in numl3er as compared with the bidentate 

 inequi-anchorate ones ; both forms are very minute and 

 require a power of five or six hundred linear to dis- 

 tinctly define their forms. 



The number of the varieties in the forms of the 

 spicula, not less than seven, and the profusion in which 

 they are supplied to the tissues renders this species a 

 very remarkable and instructive one. 



Since Mr. Norman's specimen was drawn on stone I 

 have found among my store of unexamined specimens 

 a much finer one than that which has been figured. It 

 is two and a half inches in height, two in breadth, and 

 one and a quarter inch thick. In its external characters 



