100 SILICEOUS SPONGES. 



dermal layer, which is formed of an extremely minute and delicate spicular reticu- 

 lation, extends alike over this supplemental skeleton as well as over the front surface 

 of the true wall. 



The characters of Stauronema appear to me to exhibit a closer alliance to the 

 family of the Euretidae than to the family of the Mellitionidae, in which Prof. Zittel*, 

 relying upon the descriptions of Prof. Sollas, has placed the genus. 



Prof. Sollas states that his specimens came from the Gault of Folkestone ; but the 

 numerous specimens in the Museum collection from the same locality, are, according 

 to the opinion of Mr. E. Etheridge, sen., all derived from the Upper Green Sandf, 

 and as Sollas's specimens were supplied to him by a local dealer, and were not 

 collected by himself, it seems probable that they also may have been obtained from 

 the Upper Green Sand, and not from the Gault. 



Distribution. Upper Green Sand: Folkestone; near Eastbourne. Chalk Marl : 

 near Ventnor, Isle of Wight ; Barbara. Craie Chloritee : Cap la Heve. 



Stauronema planum, Hinde, n. sp. (Plate XXIV. figs. 2, 2 a, 2 b, 2 c.) 



Sponge disk-shaped, with a circular outline ; the upper surface nearly flat, the 

 under surface slightly convex, with concentric rounded ridges and furrows. There 

 is no indication of a stem or point of attachment. The margins are rounded and 

 slightly curve downwards. The width of the only specimen at present known is 

 70 mm. In the central portion the wall-plate is 12'5 mm. in thickness and near 

 the margin 6'3 mm. 



The upper surface of the sponge is reticulate, with circular or ovate canal-apertures 

 about 1 mm. in diameter and about 1'3 mm. apart from each other. The canals are 

 slightly curved and appear to terminate blindly. No special canals are distin- 

 guishable on the under surface of the sponge. 



The sponge-wall is composed of a regular meshwork of robust spicules with solid 

 nodes; the distance between the nodes is 'ob mm. The interspaces between the 

 mesh are subquadrate or nearly circular. The upper surface exhibits traces of a 

 finely reticulate dermal layer, which apparently extended over the canal-apertures. 

 The under surface also shows a delicate dermal layer of reticulate spicules, but its 

 state of preservation is insufficient for a close determination. 



This species diff"ers from S. Carteri, Sollas, in its form and in the absence of a 

 supplemental skeleton ; but it resembles that species in the character of the spicular 

 skeleton of the wall and the disposition of the canals. 



The non-development in this species of the supplemental skeleton or posterior 



* Neues Jahrbuch, 1877, p. 359. 



t Mr. F. G. H. Price also quotes this species from the Upper Green Sand or lower division of his Chalk 

 Marl at Polkestone, and he names this division the Stauronema-7,one. No mention is made of its ocenrrence 

 in the Gault. (Quart. Journ. Geol. Soc. 1877, vol. xxxiii. p. 434.) 



