M. K. A. Zittel o??. Fossil Lithistidce. ^11 



ing into a small common depression or elevation. Oscula often 

 stellate in appearance, owing to fine radial furrows on the sur- 

 face of the true skeletal mass. Besides the oscula the surface 

 under the covering layer is furnished with fine pores, the 

 orifices of small radial canals. A few fine vertical tubes run 

 through the whole sponge-body in the direction of its axis. 

 Skeleton of small distinctly quadriradiate corpuscles with a 

 short axial cross ; arms smooth, strongly ramified at the ends. 

 The nearly dense covering layer is formed of very small, 

 closely interlocked, strongly branched, irregular lithistid cor- 

 puscles, and is easily scaled off. No special surface-spicules 

 observed. 



*1. Aster ospongia Icevis, Rom. Spongit. xix. 2. Guvieri- 

 Planer. 



*2. Asterospongia suhramosa^ Rom. ib. xix. 3. Quadratus- 

 chalk. Sutmerberg, Ahlten. 



*3. Stellispongia verynicosa^ Rom. ib. xvii. 5. Quadratus- 

 chalk. 



4. 8iphonia ramosa, Mich. Ic. xxviii. 5 ; Court. Ep. 

 xxiv. 1. 



*5. Tremospongia clavata, Rom. Spong. xiii. 13. Cuvieri- 

 Planer. 



Thecosiphonia, Zitt. 



Lymnorea p. p., Tremospongia, F. A. Rom. 

 Tremospongia, Gein. (non D'Orb.). 

 Diestosphecion p. p., Cytorea Pom. 

 Pohfjerea p. p., From. 



Sponge simple or compound, individuals large, elongate, 

 top-shaped or cylindrical ; vertex with a shallow depression, 

 into which opens a bundle of vertical tubular canals. Of these 

 canals the uppermost run nearly parallel with the periphery, 

 causing radiating furrows on worn specimens ; those in the 

 middle traverse the sponge nearly perpendicularly. There 

 are also radial canals running obliquely inwards and down- 

 wards, the round ostia of which are scattered over the surface, 

 which is rough, with crooked furrows and pits. Base simple 

 or with root-like processes, coated, as well as a larger or smaller 

 part of the sponge-body, with a dense siliceous covering layer. 

 In compound stocks this epitheca unites all the individuals. 

 Skeletal elements of considerable size, regularly four-armed ; 

 the arms smooth, with ramified ends. Bacillar spicules scat- 

 tered in the skeleton. 



This genus is nearly allied to Siphonia and Jerea^ but is 

 distinguished by its strongly developed covering layer, and 

 its larger and more regular skeletal elements. Grood figures 

 are given by Quenstedt (Petr. cxxxiii. 8-11). 



