207 



SUPPLEMENT. 



Since the first part of the work was in type fresh additions have been made to the 

 Museum Collection, including some new species, the descriptions of which, as they 

 could not be inserted in their proper systematic position, are here appended. 



Division I. SILICEOUS SPONGES. 



Order M ON ACTINELLI DiE. 

 Genus HAPLISTION, Young and Young, 1877. 



Haplistion fractum, Hinde, n. sp. (Plate XXXVIII. figs. 4, 4a.) 



In the fine collection of detached sponge-spicules which Mr. James Bennie very 

 generously forwarded to me for examination, I found several small fragments of a 

 fibrous sponge, resembling, as regards their siliceous condition, the spicules of the 

 Hexactinellid sponges associated with them. The largest of these fragments only 

 measures 5 mm. in length and thickness; it consists of irregularly anastomosing 

 cylindrical fibres from "14 to "5 mm. in thickness, which form an uneven meshwork 

 with circular or elongated interspaces about '6 mm. in width. The fibres appear in 

 fractured surfaces to be solid throughout, and the interior portion only exhibits a 

 fine granular structure. The outer surface, on the other hand, is covered with a 

 layer of simple spicules, which, though generally arranged in the direction of the fibre, 

 are not parallel with each other. The spicules, when examined under the microscope, 

 present uneven, ill-defined outlines, but they appear to have the form of fusiform 

 acerates. The longest measured is •32 mm. in length by "03 mm. in width. Whether 

 their surfaces were primarily smooth or spinous it is impossible to determine. 



There can scarcely be a doubt that the fibres were originally built up throughout 

 of spicules similar to those which are now exposed on their exterior surfaces, and 

 that by fossilization the interior spicules have been undistinguishably fused together. 

 Their resemblance in mineral condition to the spicules of undoubted siliceous sponges 

 in the same deposit points to the conclusion that they were also originally siliceous. 



