50 SILICEOUS SPONGES. 



of these canals also extend into the stem. Numerous, closely set, arched canals, 

 ■5 mm. wide, extend from the lateral surface towards the central portion of the 

 sponge. The surface-openings of these lateral canals are formed by the irregularly 

 shaped interspaces of the mesh. There are also numerous horizontal canals in the 

 stem of the sponge. 



The spicules of the body are robust, smooth, and irregularly branching, and about 

 "135 mm. in thickness. Some of the spicular arms gradually taper towards their 

 extremities ; in others, however, the extremities are expanded in a similar manner to 

 those of the genus Lyidnim. The spicules of the stem are slender, elongate, thread- 

 like, with branching ends ; they are loosely intertwined together in the direction of 

 their length. No surface-spicules have been noticed. 



This species is apparently abundant and generally well preserved. It is very 

 probable that the figure given by Parkinson [loc. cit.) is of a sponge belonging to this 

 species, though he makes mention of a large central cavity in the interior, of which 

 there is no evidence in the figure. Michelin refers the form figured by Miss Benett 

 to his Jerea elongata ; but the spicular structure of the two is altogether diff'erent. 

 Some examples resemble in appearance the figure oi Jerea iryriformis, Lamx. Exp. 

 Method, t. 78. f. 3 ; and they have apparently been referred to this species in Morris's 

 Catalogue. There is, however, no resemblance in their spicular structure, as, 

 according to Prof. Zittel, Jerea jtyriformis belongs to the Tetracladina family. 

 Prof. Morris also designates the sponges figured by Miss Benett in plate x. Cat. 

 Org. Eem. by the name of Jerea Carteri, but no reference is given to the author of 

 the specific name ; and on this account, and on the further fact that in this plate two 

 different species are figured, whilst it is not stated to which the /. Carteri applies, I 

 have not retained that term for the present species. 



Notwithstanding the variety of form and size in the examples which I refer to this 

 species, there exists such a close resemblance in their canal and spicular structures 

 that I do not see any ground for placing them under more than one species. 



Distribution. Upper Green Sand : Warminster ; Canamore quarry, near Crockerton. 



Genus HOLODTCTYON, Hiude, n. g. 



Sponges inverted, conical, or irregular in form, with rounded or flattened summits, 

 and stems with branching processes. In the centre of the summit there is a shallow 

 cup-shaped or cylindrical cavity, which appears to extend only to a short distance into 

 the sponge. 



The skeleton consists of a meshwork of smooth, irregularly branching spicules ; 

 the spicular arms either attenuated or with a spoon-shaped or elongated expansion 

 at their termination. No canals appear to be present. 



I propose this genus to include a small group of sponges which closely resemble 



