520 ARTHUR WENDY. 



II. The Genus Quasillina, Norman. 



The only species of this genus as yet described is Bower- 

 bank's Quasillina (Polymastia) brevis, a common Shet- 

 land form, living in moderately deep water. As the somewhat 

 complicated history and synonymy of this Sponge have lately 

 been fully treated of by various authors/ I need not enter 

 into the question here, but will proceed at once to the descrip- 

 tion of its general form and minute anatomy. 



Quasillina brevis, Bowerbank sp. 



External Characters. — Externally the Sponge is seen to 

 consist of a usually somewhat flattened, oval body, perched on 

 the summit of a short stalk (fig. 8). At its lower extremity 

 the stalk is somewhat expanded, and the expanded portion is 

 generally attached to a small pebble. At its upper extremity 

 the body terminates in a slight mammiform prominence, at 

 the summit of which there is a single minute osculum (figs. 

 8 and 9, o.). 



The osculum is usually so much contracted and so difficult 

 to make out that its existence has, until quite recently, been a 

 matter of some doubt ; and Vosmaer, 2 who has given by far 

 the most complete account of the genus yet published, observes 

 that he " never saw an opening at the top larger than those 

 where the sea-water enters." Ridley and Dendy 3 have, how- 

 ever, demonstrated that an osculum is, at any rate sometimes, 

 present, and my recent researches on the arrangement of the 

 canal system in the body of the Sponge justify us in assuming 

 that there is always one, although it is frequently found more 

 or less completely closed up in preserved specimens. 



According to Vosmaer (loc. cit.) the general shape of the 



1 Vide Ridley and Dendy, ' Report on the Monaxonida of the "Challenger " 

 Expedition,' p. 225. 



3 'Sponges of the "Willem Barents" Expedition, 1880-81,' p. 20. 



3 « Report on the Monaxonida of the " Challenger " Expedition,' p. 226, 

 woodcut, fig. 10. 



