35 



PLATE XIV. 



TETHEA CRANIUM, Lamarck. 



Yol. ii, p. 83, ' Mon. Brit. Spongiadse.' 



Fig. 1. Represents an average-sized specimen of 

 the sponge parasitical within an incomplete cup-shaped 

 specimen of Isodictya infundibuliformis. Natural size, 

 drawn from the specimens in the condition in which 

 they came from the sea, having been preserved in a 

 saturated solution of salt in water. 



Fig. 2. From young specimens of the same two 

 sponges, represented by fig. 1, in the condition in 

 which they came from the sea. Natural size. 



This parasitical habit of Tethea cranium, locating 

 itself within the cup of I. infundibuliformis, is by no 

 means of uncommon occurrence. 



Fig. o. An ovate form of T. cranium from a 

 specimen in the condition in which it came from the 

 sea. Natural size. 



Fig. 4. A section of a specimen of T. cranium at 

 right angles to its long axis, exhibiting the mode of 

 disposition of the skeleton fasciculi and numerous 

 gemmules embedded amid the tissues. Natural size. 

 From a wet specimen. 



Fig. 5.- -A group of minute, sigmoid, bihamate 

 spicula from the sarcodous membranes of the sponge. 

 X 1166 linear. 



These remarkable spicula eminently characterise the 

 species. There is. a sponge of the same genus from 

 the Antarctic regions, T. simillima, Bowerbank, MS., 

 which very closely resembles the anatomical struc- 

 tures of T. cranium, but differs from it in the total 

 absence of the sigmoid bihamate spicula. 



