502 DR. J. E. GRAY ON SPONGES. [May 9, 



having perfect faitli in Mr. W. Lens Aldous's accuracy. I can speak 

 of the accuracy of the plates of both these authors from the result 

 of my own observations ; and having full reliance on them, they seem 

 to be as available for my purpose as if I had myself repeated all their 

 researches. 



The arrangement here proposed is to be regarded as an attempt to 

 divide the sponges into groups and genera, so as to enable the stu- 

 dent to discover the name and alliance of the species under his exa- 

 mination, vidiich I have been repeatedly told the [preceding systems 

 have failed to effect. It is only a prodromus, and a very imperfect 

 one, requiring revision, correction, and extension. For example, 

 the large reticulated horny sponges, which form the greater part of 

 collections in museums, and the external forms of which have been 

 figured in Esper's, Duchassaing and Michellotti's, and several other 

 zoological works, require to be microscopically examined and syste- 

 matically described. 



The British Museum have received from Dr. Oscar Schmidt 

 typical specimens and preparations of the spicules of almost all the 

 species he has described from the Adriatic Seas. 



The class is divisible into two subclasses, according to the chemical 

 constituent of the skeletons ; in one the spicules are calcareous, and 

 ill the other when present siliceous, or more or less mixed with a 

 horn-like animal material. 



Subclass 1. PORIPilORA SILICEA. 



The sponges provided with a siliceous or horny skeleton, or with 

 a horny skeleton strengthened with siliceous spicules. 



Porifera heratosa et P.chaliniJa, "Grant, Tabular View, 18G1;" 

 Bowerbank, B. Sponges, i. p. 154. 



Porifera silicea etP. heratosa, Bowerbank, B. Sponges, i. pp. 1 55, 

 IGG. 



Synopsis of Families, 



SLCliou I. INIalacospor.e (Soft-spored Sponges). Rejvodnction 

 Lij ova contained in a thin memhranaceous ovisac vot strength- 

 ened by siliceous sjncules or by (jemmules, scattered in the 

 substance of the sponge. 



Subsection 1. Netted Sponges (Dictyospongi.e). Skeleton formed 

 of a continuous siliceous or horny network. 



Order I. CORALLIOSPONGIA. Sponges hard, coral-like, entirely 

 formed of siliceous spicules anchyiosed together by siliceous 

 matter into a network. Mass covered with a thin coat of sarcode 

 when alive. 



Fam. 1. DACTYLOCALYCiDiE. Spouge massivc, expanded or flabcl- 

 late, reticulate, angular. 



