FOSSILS OF THE C A. M B H I A. 1ST . 



PROSPECT MOUNTAIN GROUP. 



PORIFERA. 

 Genus PROTOSPONGIA Salter. 



Protospongia fenestrata Salter. 

 Plate ix, figs. 5, 5 a, b. 



Protospongia fenestrata Salter, 1864. Quart. Jour. Geol. Soc., vol. xx, p. 238, pi. 13, 



fij?. 12 a, 6. Ibid., Cat. Cambrian and Silurian Fossils, p. 



3, 1873. 

 Hicks, 1874. Quart. Jour. Geol. Soc., vol. xxvii, p. 401, pi. 



1(1, fig. 20. 

 Zittel, 1877. Abh. dor K. bayer. Akademie der Wiss. 2 CL, 



xiii ; Bd. " Studien ii, fossile Spongien" (p. 45, sep. copy). 

 Carter, 1877. Ann. and Mag. Nat. Hist., ser. 4, vol. xxv, p. 177. 

 Brogger, 1878. On paradoxidesskifrene ved Krekling. Sep- 



arataftryk af Nyt Magazin for Naturvidensk. vol. xxiv, i, p. 



20, t. 6, f. 14. 

 Sollas, 1880. Quart. Jour. Geol. Soc., vol. xxxvi, p. 362, figs. 



1,2. 



Koemer, 1880. Leth. Geogn., 1 Th. p. 316, f. 59. 

 Hinde, 1883. Cat. Fossil Sponges, p. 129, pi. xxviii. fig. 2. 



Mr. Salter originally described this interesting sponge as having a 

 loosely reticulate skeleton formed of very large cruciform spiculse, the 

 branches of which cross each other at an angle of 80, and only in one 

 plane, no ascending or descending branches rising from the point of con- 

 junction. The angles occasionally vary, but not much. 



More perfect specimens obtained by Dr. Hicks show the spiculse to be 

 quadriradiate, slightly raised at the center and formed of four nearly cylin- 

 drical rays. 



The skeleton, as described by Mr. Sollas, is composed of large primary 



spiculse with the interspaces filled in by three series of spiculse, each 



11 



