PLATE LXXVI, 22-5 



Colour. — In spirit dull, oclireous yellow. 



Habitat. — Diamond Ground, Hastings ; H. Ridley. 

 Jersey, Rev. A. M. Norman. 



Examined. — In spirit. 



The simplicity of the structure of this species, and 

 the close approximation of its spicula in size and pro- 

 portions to those of several other species in the same 

 section of the genus, renders it rather a difficult task 

 to discriminate the difference existing between them. 

 Although so closely approaching several congenerous 

 species, I have been quite unable to assign it to any 

 one of them. 



It differs from I. McAndrewii in having the spicula 

 rather shorter and stouter in their proportions, and in 

 having the ^^rimary lines of the skeleton more abun- 

 dantly spiculous, the lines being three, four, or more in 

 thickness ; while those of /. McAndrewii have rarely 

 more than two fasciculated in the primary lines ; nor 

 is the skeleton tissue in that species so compactly 

 constructed. The spicula in the two species very 

 closely resemble each other in form, and vary but little 

 in their average length, which is greatest in I. McAn- 

 dretvii; the slight hispidation of its surface and the 

 conical fistulous oscula of the last-named sponge also 

 serve to further separate the two species. 



The form and proportions of the spicula in /. ohscura 

 veiy closely resemble those of I. cinerea, but in the 

 latter species the primary lines of the skeleton are uni- 

 spiculous, and there is the same disjoroportions in the 

 comparative length and stoutness of the skeleton 

 spicula that exists in I. MeAndreivii. 



In I. sinvplcx the skeleton spicula are of the same 

 shape and length as those of I. ohscura, but they are 

 very much more slender in their degree of stoutness ; 

 and the surface of /. ohscura has no indication of 

 tuberous projections ; nor is the surface minutely 

 hispid as in I. simplex. 



I obtained the type-specimen of this species from 

 Mr. Ridley. It was brought up by one of the 



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