18 



Class SPONGIiE. 

 Division I. SILICEOUS SPONGES. 



Order MO N ACT INELLID^, Zittel. 



Genus CLIMACOSPONGIA, Hinde, gen. nov. 



Sponges subglobate, sessile, composed of elongate acerate spicules, which radiate 

 upwards from the base to the circumference, and are arranged so as form a closely 

 disposed series of radiating canals, which open at the surface. There are also acerate 

 spicules disposed horizontally so as to cross the vertical spicules at right angles, thus 

 forming an open tissue with rectangular interspaces. 



The only fossil sponge with which this genus can be compared is the Pulvillus 

 Thomsonii, Carter (Ann. & Mag. Nat. Hist. ser. 5, vol. i. p. 137, t. x. f. 1-6), which 

 is also composed of long acerate spicules ; but these do not appear to have the same 

 arrangement, or to be crossed horizontally by other spicules, as in the present genus. 

 The figure given by Carter of the vertical section of Pulvillus differs altogether from 

 the vertical section of Climacospongia, 



CLIMACOSPONGIA RADiATA, Hhide, sp. nov. (Plate I. figs. 1, \a.) 

 The only examples of this sponge in the Museum are portions of two individuals 

 which have been fractured in a vertical direction. The sponges are from 30 to 

 40 millim. in diameter. They are preserved in a silicified matrix ; the exterior is 

 rough and weathered, so as to show the canal-apertures only in a few places. In 

 the vertical section the radiating spicules are in part siliceous, in part replaced by a 

 reddish earthy material, probably iron peroxide ; the transverse spicules are mostly 

 replaced by the peroxide, or shown by the impressions in the matrix. The canals 

 are either subangular or circular in section, and 0'75 to I'o mm. in width. They 

 are formed and bounded by long acerate spicules, disposed vertically, sometimes in 

 a single series ; sometimes two or three spicules are side by side. The ends of the 

 spicules overlap each other, but they do not appear in any way to be attached 

 together. The vertical spicules are straight, or occasionally slightly incurved, and 

 nearly cylindrical. Near the extremities they taper very gradually. Their surfaces 

 appear to be smooth. The longest measured is 3-5 mm. The spicules of the 

 transverse series are not clearly shown in a vertical section ; they appear to be of the 

 same character as the vertical spicules, and they cross these latter nearly at right 



