32 Die Silurische Fauna des Westlichen Tennessee. 



under the name Sij)hon{a prcemorsa. The decidedly free, not attached 

 condition, is the princii^ul character which separates this genus from 

 the genuine S'qjhonia of the later formations, and justifies the creation 

 of a separate genus. Besides, the body being composed altogether of 

 little regular stars, connected together, is a peculiarity not found either 

 in the genuine Siphonia, nor in any other sponge genus of the later 

 formations. 



The genus, with its not numerous species, appears to be limited to the 

 upper division of the Silurian Group. 



ASTYLOSPONGIA rK.EMORSA (Gold.) 



Siphotnn prccmorsa, Goldfuss Petref. Germ., 1, 17, t. G f . 9 (1826). 



" " Hisinger Leth. Suec, 94, t. 26 f. 7 (1837) 



" ". Eichwald Silur. Schichtensyst. in Esthland, 209. 



" '• Maximilian, Herzog von Leuchtenberg. Beschreibung 



einiger neuen Tliierreste der Urwelt aus den Silu- 

 risclien Ivalkschichten von Zarskoje Selo.. St. Pe- 

 tersburg (1824). 



" " Fred. Rcemer in Leonh. u. Bronn's Jahrb. (1848, 684). 



" " Ferd. Ecemer in Lethje geogno-st. ed. 3, Th. ii., 154 



t. 27, f. 21 (1852-1854). 



" ezcavata, Goldfuss Petref. Gerra. 1, 17, t. 6 f. 8 (1826). 



" " Bronn. in Leth. geogn. ed. 3, Th. v., 75 (1851-1852). 



" stipitata Hisinger Leth. Suec. 94, t. xxvi., f. 8. 

 Jerea excavuta, D'Orbigny Prodr. de Pal. strat. ii, 286 (1850). 



A free, almost globular sponge, with a truncated and disk-formed, 

 depressed crown, and a completely rounded or somewhat truncated 

 underside. The concave crown exhibits a number of larger openings, 

 the mouths of perpendicular pipes. From the edge of the crown there 

 radiate over the sides irregular and partially branching furrows. 

 Although a proper epitheca is never observed, yet, in the specimens 

 from Tennessee, the lower end is sometimes truncated by a small, smooth, 

 circular surface, on which the body rests. In older specimens the fur- 

 rows radiating from the crown are often much deeper and broader. 

 The whole body is then often no longer perfectly globular, but some- 

 what depressed. The whole lower half of the sponge is, moreover, 

 sometimes bordered with wart-like prominences. 



Several specimens, which I caused to be cut and polished, have 

 shown a very peculiar constitution of the inner texture of this sponge. 

 The whole mass consists of small, very regular, star-formed bodies, 

 with six rays, which may be seen with the unaided eye, but more dis- 

 tinctly with a glass, and which are so connected together that a ray 

 from one star runs directly into the ra}' of the star next to it. Be- 

 tween the stars, which are composed of opaque siliceous matter, there 



