STAUEO^'EMA. — SESTRODICTYON. 101 



mass, which is such a prominent feature in the type of the genus, does not appear 

 to me to be of sufficient importance by itself to justify placing this form in a separate 

 genus, and it would be preferable to extend the definition of Stauronema so as to 

 include sponges in which a supplemental skeleton is not present. 



The only example of this species has the spicular structure replaced by calcite, 

 and by a dark material, probably iron peroxide. This dark substance has infilled the 

 canals of the hexactinellid spicules, which are thus distinctly shown, even when the 

 spicular arms themselves have been obliterated. 



Distribution. Grey Chalk : Folkestone. 



Staueonema compactum, Hinde, n. sp. (Plate XXV. figs. 1, la, Ih, Ic, Id.) 



Sponge apparently forming an ear- or fan-shaped expansion, growing from a small 

 rounded basal process; the wall is between 6-8 and 8 mm. in thickness. The only 

 specimen is the lower portion of an example, and measures 43 by 25 mm. 



Both surfaces of the sponge-wall are furnished with oval canal-apertures from 

 •75 to 1 mm. in diameter, arranged in decussating lines. On what appears to be 

 the inner or upper surface these canal-apertui'es are about 2 lines apart, and the 

 interspaces between them consist of a thickened reticulate mesh with definite 

 circular pores. On the ojjposite surface the canal-openings are completely covered 

 in the lower part of the wall by a dermal layer of thickened irregular spicular 

 tissue ; somewhat higher the canals are only bridged over by this tissue, but not 

 concealed. The canals are blind, and follow a slightly curved direction througli 

 the wall. 



The spicular mesh of the interior of the wall is composed of robust spicules with 

 compact nodes ; the arms are apparently smooth ; the distance between the nodal 

 centres is 'SS mm. The interspaces of the mesh are circular or oval. 



Quenstedt* has figured a sponge from the Lower Planer of Bohemia, under the 

 name of Sci/pkia tenuis, which in the characters of the dermal layer and the canal- 

 structure closely resembles the present species ; but according to Quenstedt its 

 spicular nodes are partly octahedral and partly solid, whereas in the present form 

 the spicular nodes are compact throughout. 



Distribution. Gres vert (Upper Green Sand): France] 



Genus SESTRODICTYON, Hinde, n. g. 

 Sponge funnel-shaped, apparently by the infolding and coalescence of a plate-like 

 wall. The wall is perforated by numerous canals, arranged in a generally linear 

 direction, and occasionally decussating. The skeletal mesh is composed of robust 

 spicules with compact nodes, which form a very regular quadrate mesh with small ■ 

 circular interspaces. No dermal layer ajjpears to be present. 



• Petrof. Bd. 5, p. 457, t. 137. f. 4. 



