TETRAXONIDA. 21 



Island. The typical form came from oti' the Rio de la Plata, 600 fms. ( Voy. ' Challeno'er '). 

 Topsent records it from near Fayal, 130 metres, and 55 miles N.N.W, of Fayal, 1900 

 mfetres. 



PSKUDOSUBERITES HYALINUS. 



(Plate XXVI., figs. 7a-b.) 



1887. Hymeniacidon ? /iyaZma Ridley and Dendy (15. p. 1G8). 

 1898. Pseudosuhi^rites hyaJinus Topsent (27. p. 103). 

 1900. Pseudusiiberites hyalinus Topsent (28. p. 170). 



The single specimen is of a compressed cylindrical shape, 6 cm. long and 8 mm. in 

 diameter. The colour is white. There does not appear to be any area of attachment, 

 both ends being complete and rounded. Two thin walled oscules, each about 2 mm. in 

 diameter occur along one edge of the specimen, the exhalant canals proceeding towards 

 them being clearly visible. On one side of one of the oscules is a wall of .spicules 

 formed by a continuation and flattening out of some of the lateral or secondary skeletal 

 bundles. 



A longitudinal section shows clearly a central loose core of longitudinal fibres each 

 about 100 /i thick, anastomosing .slightly and giving off at right angles bundles of 

 spicules which support the dermal membrane ; in the thinner parts of the specimen 

 these bundles are one spicule in length, but at the thickest part they may be two or 

 three .spicules in length and traversed by longitudinal bundles. The original 

 specimens obtained from Kerguelen by the ' Challenger' are " massive and amorphous," 

 and the skeleton is more of the " halichondrioid type," but here also the longitudinal 

 bundles and those sujjporting the dermal memlirane can be distinctly made out. In 

 the Antarctic specimen the cylindrical shape has brought about the more regular 

 arrangement. The Mediterranean .sponge, identified by Topsent (27. p. 103) as 

 P. hyalinus, is massive, amorphous, and encloses foreign bodies. The surface is 

 mammillated and a little hispid, this condition resulting from the prolongation of the 

 lateral bundles or fibres of the skeleton. The tyles of the Antarctic form are about 

 1000 X 19 fi, those of the Kerguelen form 1100 x 25 jjl, and those of the Mediterranean 

 form from 300 x 10 /x to 1200 x 26 /x. 



An interesting feature is that all the spicules point in a direction upwards or 

 upwards and outwards. 



Two other species of Pseudosuherites are P. sulphnreus (Bowerbank), from the 

 seas of N.W. Europe, and P. aiidrewsi, Kirkp. (9. p. 135), from Christmas Island ; this 

 last species forms a cake-like crust, and its spicules are much smaller than those of 

 P. hyalinus, being only 350 x 6 /x. 



The specimen was dredged from W.Q. No. 10 hole, 130 fms. 



The species has been found off S.W. Patagonia, Voy. 'Challenger,' St. 311, 175 fms., 

 and off the Mediterranean coast of France in 500 to 600 metres, Topsent. 



