HETEEOSTINIA. 53 



Genus HETEKOSTINIA, Zittel, 1878. 



Hetekostinia obliqua, Benett, sp. (Plate X. figs. 2,2 a, 2b, 2 c.) 

 1831. Polypothecia obliqua, Benett, Cat. Org. Rem. Wilts, t. 8. f. 1. 



Body of sponge consisting of a variously convoluted plate-like wall, either platter-, 

 ear-, or fan-shaped, and not infrequently, by the coalescence of the wall-margins, 

 becoming either cup- or open funnel-shaped. The body is usually supported by one 

 or more rod-like short processes, which are sometimes compressed so as to form 

 semipalmate expansions. The walls are from 7 to 10 mm. in thickness. The 

 examples vary greatly in size: a large cup-like specimen attains a width of 85 mm., 

 and one platter-shaped form is 200 mm. in extension. 



On both surfaces of the wall there are numerous irregularly disposed circular 

 apertures, about "7 mm. each in width, and from one to three diameters apart ; 

 between these circular apertures are the irregular openings formed by the spicular 

 mesh. No indications of canals in the interior of the wall have been preserved in 

 the specimens which I have examined, though occasionally the sponge-wall is pene- 

 trated by cavities which appear to be due to external causes. 



The spicules of the body-skeleton are relatively large, vermiculate, branched, and 

 attached to each other by their slightly expanded extremities. In the best preserved 

 specimens the surface of the body-spicales exhibits a very fine, minute granulation ; 

 in other specimens the spicules appear to have smooth surfaces, but the smoothness 

 may be due to the wearing-off" of the fine granulation by fossilization. In all other 

 respects the sponges with the granulated surfaces to the spicules and those with 

 smooth surfaces are precisely similar, so that I find it impossible to constitute two 

 species based on this feature alone. The body-spicules vary in thickness between 

 •112 mm. and -1575 mm. The spicules of the stem are thinner and more elongated 

 than those of the body, and they are connected by being adpressed and intertwined 

 together. The sponge appears to have possessed a dermal layer consisting of trifid 

 spicules Avith horizontally expanded, bifurcated, and pointed head-rays. This dermal 

 layer is but very rarely preserved. The minute irregularly shaped spicules which, in 

 the type of the genus, intervene between the larger mesh-spicules are also very rare, 

 and I have only detected their presence in portions of the stem. 



In the mode of attachment of the body-spicules of this species by their slightly 

 expanded extremities, these sponges resemble those of the genera Lyidlum and 

 Pachypoterion ; and I was at first disposed to place them under the former of these 

 two genera. There are slight evidences, however, of the presence of the minute 

 spicular bodies which constitute the distinguishing character of the genus Hetero- 

 stinia, Zitt. ; and Prof. Zittel, who has examined one of these sponges, pronounces it 

 a genuine example of this genus. In this case, the definition of Ileterostinia will 



