[DAWSON] FOSSIL SPONGES AND OTHER ORGANIC REMAINS 



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Order SILICEA. 



Suborder Hexactinellida. 



Group Jjyssakina. 



Familjj Protospongid.e, Hinde. 



Genus PEOTOSPONGIA, Salter. 



This genus was established by the late Mr. Salter from some remains 

 of lattice-like spicular bodies found in the Middle Cambrian of Wales, and 

 which, though fragmentary and obscure, that eminent naturalist was 

 able to refer to the group of Siliceous sponges. The genus includes several 

 of the Metis species, which have enabled us to complete the characters of 

 Salter's genus. 



1. — Protospongia tetranema, Dawson.' 

 (Figs. 1 to 5. PI. I., Figs. 1 and 4.) 



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Fig. 1. — Proiospongin tetranema. 

 A small specimen restored. 



Fig. 2. — Protospongia tetranema. Anchor- 

 iug-spicules slightly enlarged. 



In the specimens in which the outline of the sponge has been pre- 

 served, the body apj)ears to have been rounded or broadly oval. There 

 was an aperture or osculum at the summit, though it can be distin- 

 guished only in a few specimens. The wall of the sj^onge appears to have 

 consisted — as in the other species of this genus — of a single layer of 

 cruciform spicules of various dimensions, disposed so as to form a frame- 

 work of quadrate or oblong interspaces. The rays of the larger spicules 

 constitute the boundaries of the larger squares ; but owing to decay 



1 The characters of this and several of the following species were given in "Notes 

 on Specimens in the Peter Redpath Museum, " and in the Transactions of the Rojal 

 Society, 1889. 



