84 SILICEOUS SPONGES. 



also exposed on the surface elongated irregular filiform spicules. The entire sponge 

 appears to have possessed a smooth dermal layer of horizontal spicules with laciniated 

 arms; these heads are about '9 mm. in width. I have not been able to discover the 

 character of the shafts of these spicules. 



This species differs from the two preceding, not only in its outer form, but in the 

 larger size of the body- and dermal spicules. 



Distribution. Upper Chalk: Beckhampton, Wiltshire {Cunnington coll.). 



Eagadinia clavata, Hinde, n. sp. (Plate XIX. figs. 4, 4 o, 4 6, 4 c.) 



Sponges u'regularly rod- or club-shaped, often with stumpy processes and nodose 

 outgrowths. Very variable in size, sometimes reaching to 100 mm. in height and 

 from 13 to 31 mm. in thickness. 



The surface appears to have been covered with a smooth dermal layer ; where this 

 is absent, surface-canals, about '6 mm. in width, are exposed, closely seaming the 

 exterior of the sponge. 



The interior skeleton is composed of distinctly annulated spicules similar to those 

 of R. coiiipressa. The spicules of the dermal layer have narrow laciniated head-rays ; 

 they are about '5 mm. in extension, and so disposed that there are minute interspaces 

 between the rays or ai"ms. When the spicules have fallen from the surface of the 

 sponge, it often happens that the material filling these small interspaces stands out 

 as so many minute tubercles. 



This species is readily distinguished from others of the genus by its peculiar form. 

 All the examples have been procured from the interior of flints, and only the spicules 

 of part of the dermal layer and the spicular structure immediately beneath this layer 

 have been preserved. 



Distribution. Upper Chalk: Wiltshire {Cunnington coll.). 



Genus PLINTHOSELLA, Zittel, 1878. 



This genus was founded on small, spherical, or irregular nodose sponges, from 

 5 mm. to 25 mm. in thickness, with an interior skeletal mesh of large irregularly 

 four-armed tuberculated spicules, and a dermal layer composed of small scaly disks 

 of irregular form. In the Museum collection and in the Jermyn-Street Museum 

 there are cup-shaped, rod- or club-like, and convoluted sponges with an interior 

 skeletal mesh closely resembling that of Pii)ithoseUa squamosa, Zitt., the type of the 

 genus. The spicules of the dermal layer of these sponges, however, vary in detail 

 from those of the type species, for they are usually disk-like with jagged edges, or 

 even occasionally lobate. This variation is not sufficient, however, to be regarded as 

 a basis for generic distinction, for in a single specimen of the typical species there 

 may be found great diversity in the form of the disks of the dermal layer. 



