550 DR. J. K. GRAY ON SPONGES. [May 9, 



Order VII. POTAMOSPONGIA. 



Ovisacs coriaceous, scattered in the tissue of the sponge, especially- 

 near the base. The cells coriaceous, with a permanent central cavity, 

 strengthened externally with superficial spicules. 



Fam. Spongillad^. 



Sponge massive or branched. Skeleton formed of a network of 

 spicula, more or less united together by horny matter ; network 

 symmetrical, four-sided. 



Living in fresh water. — Green. 



Spongilla, Lamk. A. s. Vert. ii. p. 98 ; Carter, Journ. Roy. Asiat. 

 Soc. 1849, xii. p. 1. 



Ephydatia, Lamx. ; Gray, Brit. Plants, i. p. 353. 



Tupha, Oken. 



Badagia, Buxbaum in Sprengel, Syst. Veg. iv. p. 374. 



I. The ovisacs thick, S7nooth, armed with birotate spicules, united 

 by a central shaft, placed at right angles to and extending 

 from the outer to the inner surface of the sac. 



1. Ephydatia. 



Sponge-spicules fusiform, smooth. The disk of the ovisac-spicules 

 entire or divided into lobes. 



* Disk of ovisac-spicules divided into lobes. 



1. Ephydatia fluviatilis, Bowerb. B. S. f. 217, 218 ; P. Z. S. 

 1863, p. 7, t. 38. f. 1. 



Hab. Europe. B.M. 



2. Ephydatia meyenii. Carter, Asiatic. Soc. Journ. xii. p. 4, 

 t. 1. f. 1 ; Bowerb. B. S. f. 219 ; P. Z. S. 1863, p. 10, t. 38. f. 4. 



Hab. Bombay. B.M. 



** Disk of ovisac-spicules entire. 



3. Ephydatia leidyi. 



Spongilla leidyi, Bowerb. P. Z. S. 1863, t. 38. f. 2 (disk of ovisac- 

 spicules entire, smooth). 



4. Ephydatia capewelli. 



Spongilla capewelli, Bowerb. P. Z. S. 1863, t. 38. f. 2 (disk of 

 spicules of ovisacs tubercular). 



2. DOSILIA. 



Sponge-spicules of two forms : — 1. Fusiform, smooth. 2. Cylin- 

 drical, nodulose ; central nodules extending beyond the stellate, and 

 some spherical stellates with a group of recurved hooks at the ends of 



