24 SILICEOUS SPONGES. 



Genus TETHYOPSIS, Zittel, 1878. 



Tetetopsis cretaceus, Hinde, n. sp. (Plate I. figs. 5, 6 a.) 



Sponge either compressed or growing in small upright masses of irregular outline, 

 with interpenetrating canals and passages. The sponge-tissues are composed of 

 straight, smooth, acerate spicules, pointed at both ends, and from 2 to 3 mm. in 

 length. Mingled with the acerates are a few simple trifid spicules, with short 

 slightly recurved head-rays. The spicules are disposed generally parallel with each 

 other in close juxtaposition. The surface-characters of the sponge are not preserved. 



One example of this species is preserved in the interior of a flint, and displays very 

 clearly the form and arrangement of the spicules. Another specimen is a flattened 

 mass 110 mm. in length, 80 mm. in width, and 16 mm. in thickness, which has 

 been partially dissolved out of the Flamboro' Chalk. This mass appears to be 

 entirely composed of spicules, which, however, are so altered by fossilization as to be 

 scarcely distinguishable. 



From Tethyopsis Steinmamii, Zitt.*, the only other species of the genus, this form 

 differs in the smaller dimensions of the acerate spicules, and the shorter head-rays of 

 trifid forms. 



Distribution. Upper Chalk : Flamboro', Yorkshire ; South of England. 



Genus STELLETTA, 0. Schmidt, 1866. 



Stelletta inclusa, Hinde, n. sp. (Plate I. figs. 6, 6 a.) 

 The only example of this species is preserved in the interior of a chalk flint, and 

 appears to have been originally hemispherical in form. The section shown is 

 61 mm. in length by 21 mm. in height. The sponge is composed of spicules in 

 close juxtaposition, parallel vnth each other, and disposed with an outward radial 

 direction. 



There are three kinds of spicules present: — 1st. Straight, elongated acerates, 

 nearly cylindrical throughout : these do not appear to be very numerous. 2nd. 

 Robust trifid spicules with a straight shaft, which gradually tapers from the head to 

 the pointed extremity ; the summit is somewhat flattened, the head-rays are short, 

 simple, somewhat sharply recurved, and with pointed ends. These spicules vary 

 between 2 and 4 mm. in length ; an average specimen (2-475 mm. long) has the 

 shaft 0-15 mm. wide, and measures across the head-rays 0-412 mm. The main 

 portion of the sponge is composed of these trifid spicules, which are disposed in a 

 radial direction with the heads towards the exterior. 3rd. Anchor-shaped trifid 

 spicules, with a conical bullet-shaped head, and an elongated cylindrical or very 

 gradually tapering shaft. I have not obtained one of these spicules with an entire 



* Studien, III Ab. p. 9, t. xi. f. 3. 



