SILICIOUS AND HORNY SPONGES WILSON. 309 



those portions of the chone-canals, both afferent and efferent, which 

 lie in the extra-sterrastral layer of the ectosome (ectochrote) are so 

 expanded as to have the character of ordinary subdermal spaces 

 which largely fill the ectochrote. In addition to orthotriaenes (or 

 dichotriaenes) and rhabds, the megasclere-complex frequently in- 

 cludes anatriaenes and protriaenes. The sterraster is spheroidal or 

 ellipsoidal, in some species somewhat flattened. The dermal micro- 

 sclere is a euaster. Other forms of euaster occur in the interior. 



Cydonium Flemming is b^y general consent merged in Geodia (Len- 

 denfeld, 1894; Topsent, 1904, p. 68; Dendy, 1905, p. 84; Thiele, 

 1905). Sollas in his definition of Cydonium (1888, p. 218) says the 

 oscula are sometimes the uniporal openings of excurrent chones. But 

 the species records scarcely bear out this statement, since in Geodia 

 (Cydonium) muUeri, the only form cited by Sollas as possibly hav- 

 ing uniporal efferent chones, Lendenfeld finds (1894, 1903) the 

 oscula are cribriporal. Whatever species exist with uniporal ef- 

 ferents would be referable to Sidonops, while the Cydonium forms 

 with cribriporal efferent chones are not distinguishable from Geodia. 



In some species of Geodia the incurrent and excurrent orifices are 

 not distinguishable. In other species the former are somewhat 

 larger. The excurrent orifices are typically grouped in one or more 

 restricted areas, the incurrent orifices covering the rest of the sur- 

 face. In caliculate forms the chief excurrent area is the surface of 

 the cloaca, but depressed areas on the outer surface may also be 

 excurrent (G. miilleri). In some species the two classes of orifices 

 are on opposite surfaces of the noncaliculate body (G. exigua 

 Thiele). 



The form is massive; or more or less caliculate; sometimes lobose; 

 sometimes a thick, massive incrustation. In some of the caliculate 

 forms, massive young stages are known (G. mi'dleri). Lendenfeld 

 (1894, p. 91) has shown that the caliculate forms can not be separated 

 from the noncaliculate, and hence that Sollas's definition (1888, p. 

 244) must be altered. 



In some species (G. stellata Lendenfeld, G. rohusta Lendenfeld, 

 1906) the system of subdermal spaces which largely fill the ecto- 

 chrote is divided into unit systems, each unit system representing 

 the outer (ectochrotal) horizontally expanded and branched portion 

 of a chone-canal. Every unit system is covered over by a special 

 pore area (incurrent or excurrent), and connects at its center with 

 one of the straight tubular endochonal canals which pass radially 

 through the sterrastral and innermost layers of the cortex. In other 

 species (G. philippinensis) the system of subdermal spaces is per- 

 haps not divisible into unit systems, since the dermal membrane is 

 uniformly perforated instead of being divided into discrete pore 

 areas and intervening aporous tracts; moreover the subdermal spaces 



