REPORT ON THE TETRACTINELLIDA. 
cxlvii 
In all species the trisenes usually lie with their cladi extended facially immediately 
beneath the sterrastral layer of the cortex ; sometimes but rarely the cladi enter this layer 
and are then liable to deformations, more often both trisenes and rhabdi pass through 
and project beyond the cortex, hispidating the surface. A second finer hispidation is 
frequently produced by small oxeas, which are confined to the cortex (cortical oxeas). 
Associated with these in some few instances are minute anatrisenes, which much remind 
one of the cladose tylostyles described by Dendy and Eidley in Proteleia sollasi. 
Genital Products. — Spermatozoa, but not ova, have been observed ; for an account of 
the former see Caminus (p. 216). 
Development. — The earliest form of Geodia which I have seen is a small Sponge, 
almost spherical, measuring 1'6 and 1'27 mm. along its polar and equatorial diameters; 
it occurred among the hispidating spicules of a specimen of Rhaphidotlieca marsliall-halli, 
S. Kent, belonging to the Kev. A. M. Norman’s collection of Norwegian Sponges. Com- 
paratively large as this specimen is, it yet presents points of difference from the parent 
Sponge of considerable interest : the ectosome is scarcely advanced beyond the stage of 
Thenea muricata, certainly not beyond that of Myriastra ; a thin membrane covers 
extensive subdermal cavities, just as described in the case of Stelletta phrissens, and 
chones are absent ; just above and bulging out the lower face of the dermal membrane is 
a single layer of sterrasters ; these lie more remote from one another than in the adult, 
but are united together by bundles of granular fusiform cells in precisely the same fashion : 
the sterrastral layer develops, therefore, in what corresponds to the roof of subdermal 
cavities, and thus we meet with confirmation almost amounting to proof of the con- 
clusion arrived at in the case of Stelletta phrissens, viz., that in some cases the cortex is 
a highly developed dermal membrane and the chones centrifugal extensions of the sub- 
dermal cavities. 
The Geodiidse may be classified as follows : — 
Subfamily 1. Erylina. 
The megascleres are orthotrisenes and rhabdi ; anatrisenes and protrisenes are absent. 
The somal microsclere is a diactinate aster or spherule. 
Genus 1. Erylus, Gray. 
Erylus, Gray, Proc. Zool. Soc. Loud., p. 549, 1867. 
Triate, Gray, Proc. Zool. Soc. Loud., p. 549, 1867. 
The sterraster is seldom spherical ; the somal microsclere is a centrotylote microrabdus. 
The incurrent chones are uniporal, and the oscule is the patent oj^ening of a cloaca. 
Type — Erylus mammillaris (0. Schmidt) (p. 238). 
