ASTR^OSPONGIA. — STAUEACTINELLA. 149 



from 40 to 90 mm. in width, and \from 12 to 20 mm. in thickness. The entire 

 sponge is composed of star-shaped spicules, with six flattened or rounded rays in a 

 horizontal plane ; the rays are usually obtuse at the extremities ; the centre of the 

 spicule is slightly expanded. The spicules A^ary in size : large examples are 8 mm. in 

 diameter, and the rays are -75 mm. in width. Occasionally in the rays of some of 

 the larger spicules longitudinal furrows, representing the interior canals, are exposed. 

 The spicules do not appear to have been attached together. The examples are now 

 partly altered to calcite ; even where the siliceous composition has been retained, the 

 spicules are more or less obliterated. 



Distribution. Silurian : Niagara group. Perry County, West Tennessee. 



AsTR^osPONGiA PATINA, F. Ecemer. (Plate XXXI. fig. 5.) 



1861. Astr<Bospongia patina, F. Roemer, Die fossile Fauna d. Silui-.-Gesch. von Sadewitz 

 p. 14, t. 3, f . 5 a-d. 



Sponges growing in concavo-convex disks, and sessile, the same as in the preceding 

 species. The star-like spicules vary from -36 to 1-5 mm. in diameter, and the rays from 

 •033 to -112 mm. in width. In the centre of most of the spicules is a small protu- 

 berance, representing a seventh ray at right angles to the other six. This species 

 differs from A. meniscus in the much smaller size of the component spicules. 



This species is only represented in the Museum by some detached spicules, which 

 I have discovered abundantly present in some decayed shales from the Isle of 

 Gotland, presented to me by Prof G. Lindstrom of Stockholm. The spicules are 

 now composed of calcite; their rays are flattened and obtusely terminated; the 

 surface is rough and uneven, and no traces of canals have been preserved. These 

 spicules correspond in size and form with those of the unique example of this species 

 discovered by Rcemer in the glacial drift of Sadewitz in Lower Silesia, and there can 

 be little doubt as to their belonging to a sponge of this species. The occurrence of 

 these spicules in situ further supports the conclusion, drawn from the other fossils in 

 the drift, that this deposit has been derived from the Silurian strata of the Baltic 

 basin. 



Distribution. Silurian strata of Wenlock age : near Visby, Isle of Gotland. 



Genus STAUEACTINELLA, ZUt. 1877. 



Stauractinella cretacea, Hinde. (Plate XXXI. fig. 6.) 

 1880. Stauractinella cretacea, Hinde, Foss. Sponge- Spicules, p. 70, t. 5. f. 9-11. 

 This species is based on detached hexactinellid spicules, with elongated rays 

 reaching to 2 mm. in length. There is in the Museum a subcylindrical specimen 

 from the Upper Chalk, 42 mm. in length and 34 in width, which shows on the outer 



