74 SILICEOUS SPONGES. 



exterior by wide channels; in the elongate examples the lobes are deeply constricted, 

 and no definite canals are apparent. The spicular mesh of the interior is composed 

 of four-rayed spicules, with apparently smooth arms and prominent nodes at their 

 junction with each other. A dermal layer is partially preserved, but its component 

 spicules are not recognizable. 



I propose this genus for a small group of sponges which, in external form, closely 

 resemble certain species of AstroboUa, Zittel. In this genus, however, the spicules 

 are of the RMzomorine type, whereas in Bolospongia they are distinctly Tetracladine. 

 The specimens are from the Upper Chalk of Flamborough, and, in common with all 

 the examples from this locality, their spicular structure has been mostly destroyed. 



BoLOSPONGiA GLOBATA, Hiude, n. sp. (Plate XVII. figs. 1, 1 «, 1 b.) 



Sponges subspherical, closely resembling a potato in form, the surface uneven, with 

 slight rounded elevations and intervening depressions ; in some examples there is a 

 minute peduncle not more than 5 mm. in length ; other specimens are apparently 

 entirely free. An average example is 45 mm. in diameter. 



On the surface of specimens which have been treated with acid there are exhibited 

 in places small circular apertures about 2'5 mm. in width, and occasionally a few 

 canals radiate from these over the surface. In a vertical section irregular channels, 

 6 mm. wide, and open spaces are exposed. The spicules have been replaced by 

 crystalline calcite and silica, but their rough outlines can be distinctly seen in thin 

 sections. The arms are relatively large and robust, "315 mm. in length by -067 mm. 

 in width ; some of the nodes are "27 mm. in thickness. 



Distribution. Upper Chalk : Flamborough, Yorkshire. 



BoLOSPONGiA CONSTEICTA, Hinde, n. sp. (Plate XVII. fig. 2, 2 a.) 

 Sponge elongate, consisting of a series of irregularly shaped lobes, the constrictions 

 between which extend to the central portion of the sponge. There are a few traces 

 of surface-canals ; oscules are not apparent, and the circulation seems to have been 

 carried on in the channels between the lobes. The spicular mesh is of a loose, 

 open character ; the spicules are similar to those oi £. globata. A compact dermal 

 layer apparently covered the outer surface, but the form of its spicules cannot be 

 recognized. 



There is but one specimen of this singular sponge in the Collection. It is 108 mm. 

 in length by 42 mm. in width. 



Distribution. Upper Chalk : Flamborough. 



