476 M. K. A. Zittel on Fossil Lithistidm. 



POLYJEREA, From., emend. Zitt. 



Jerea, jNlich. 



Siphonia p. p., Coiu't. 



Jei-ea p. p., D'Orb. 



Polyjerea, Dichojerea p.p., Pom. (iion Pohjjerea, Rom.). 



Sponge compound, tufted or branched, rarely simple, the 

 cylindrical or barrel-shaped individuals often united at their 

 base, with rounded vertex, in which are several apertures of 

 vertical canals, which traverse the whole sponge-body. The 

 base and the whole, or a great part, of the sponge covered 

 with a smooth siliceous epidermis, beneath which are the 

 ostia of the small radial canals. Skeleton, as in Jerea^ chiefly 

 composed of large, smooth quadriradiates, with branched ends; 

 and of very small, elegantly filigreed, indistinctly quadriradi- 

 ate, siliceous corpuscles, which lie close together at the surface 

 and form the skin. 



Increase takes place either by basal or by lateral budding, 

 producing either busby or arborescent forms. The distinction 

 from Jerea consists in the small development of the radial 

 canals and the presence of the epidermis. Nearly all Romer's 

 species of Polyjerea belong to Jerea. Polyjerea is nearly 

 allied to Thecosiphoma, in which, however, the epidermis 

 is confined to the lower part, the individuals are larger, the 

 vertical canals are much more numerous and open into a 

 depression, and the radial canals are much better developed. 



The typical species is very abundant in the Senonian near 

 Evreux. 



1. Polyjerea ramtfer a, Z'ltt., distinguished from Jerea gre- 

 garia and ccespitosa by the more distinct separation and fur- 

 cation of the branches. 



There also belong here : — 



2. Jerea arborescens, Mich. Ic. xlii. 2 a (non 2 b). Seno- 

 nian. 



3. Jerea gregarta, Mich. ib. xxxviii. 1. Senonian. 



4. Jerea ccespitosa^ Mich. ib. Ixi. 4. Senonian. 

 Siphonia arborescens, Court. Ep. xxiv. 2. 



ASTROCLADIA, Zitt. 



Siphonia p. p., Mich. 



Asterospongia p. p., Stellispongia p. p., Rom, 



CaUojerea p. p., Pom. 



Sponge cylindrical, or arborescent by dichotomous ramifi- 

 cation, massive, with no central cavity. Surface with a 

 smooth (apparently dense) covering-layer, in which are distant 

 oscula, which usually consist of some short fine tubes open- 



