Mr. H. J. Carter's Contributions to our 



illustrations, but does not appear in Dr. Wright's figure, be- 

 cause this approaches more to the embryonic form, which is 

 spherical, as evidenced by a specimen, not more than the 

 225th of an inch in diameter, which I accidentally found (and 

 have mounted) on a fragment of a linear sponge-spicule 

 dredged up from the Atlantic Ocean, where this species seems 

 as it were to swarm. Besides this the larger forms of flesh- 

 spicules which Prof. Soil as has termed " quadriradiate stel- 

 lates " and described in his paper (I c. pp. 433, 434) are in- 

 comparably more abundant than in Tethea muricata ; at the 

 same time, from what he has stated and what I myself have 

 observed, this often appears to be the effect of age; hence 

 Prof. Sollas observes (p. 433) that " it is worth noticing 

 that the quadriradiate stellates are the last spicules to appear 

 in the development of Thenea Wallichii [WyviUethomsonia 

 Wallichii] ; so that very young examples of this species are 

 not distinguishable from T. muricata" 



In the most perfect form of WyviUethomsonia Wallichii 

 that I could find, which, as just stated, is that now before 

 me, the summit is covered with fine anchor-spicules amongst 

 the projecting points of the body-spicules, while the radical 

 cords extended from the other end are of course composed of 

 much stouter ones, so that, as in all the Pachytragicla, they 

 may be considered part of the normal spiculation, although, 

 from what has been stated, they may not be always present ; 

 that is to say an absence of the anchor-heads is of no spe- 

 cific value. As regards the dimensions of this little specimen, 

 it is \\ inch long, including the radical cords (four in 

 number), of which the body forms one half. The pileus 

 or hat is l-12th of an inch in vertical diameter, and the 

 cribriform lace-like dermal structure between it and the rest 

 of the body about the same ; while the widest part of the 

 body is the pileus, being now, in the compressed state of the 

 specimen, 5-12ths inch, on either side of which, i. e. above and 

 below, it diminishes to the ends respectively, the upper part 

 terminating in the broad osculum at the summit, and the 

 lower part extended somewhat over the radical appendages. 

 Interiorly the upper part of the central line is occupied by a 

 long cup-like cloaca, which opens at the summit through a 

 wide osculum, and the lower part chiefly by the ends of the 

 spicules which go to form the radical cords ; while the rest of 

 the body is traversed by a cavernous excretory canal-system 

 like that of Hyalonema, which opens into the cloaca. Thus 

 the adult form and the abundance of large fiesh-spieules chiefly 



causes WyviUethomsonia Wallichii to differ from Tethea 

 muricata. 



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