1881.] 



THE SURVEY OF H.M.S. 'ALERT.' 



12/ 



as well as relatively stouter than in our Sponge. Outward form 

 branching and fixn-shaped. Its primary-skeleton fibres are far nearer 

 together than here ; in composition they are 1- to 2-spicular in some 

 parts, 2- to 3-spicular in others, while 2 to 3, occasionally 4, is the 

 proportion in the present species. The proportion of horny matter 

 in the fibre is generally, as here, only just sufficient to bind the spi- 

 cules into a pliable fibre. 



The chief differences are shown in tabular form : — 



B. fortior is only known to me by its description, as the Museum 

 possesses no specimen of it. 



ScHMiDTiA ATJLOPORA, Schmidt, var. 



Schmidtia aidoj)ora, Schmidt, Spong. atl. Geb. p. 44, ])1. v. fig. 8. 



Thalysias subtrianguJaris, Duchassaing de Fontbressin et Miche- 

 lotti?, Spong. mer Caraib. p. 85, pi. i. fig. C, pi. xviii. fig. 1. 



Isodictya 7nirabilis, Bowerbank?, P. Z. S. 1873, p. 319, pi. xxviii. 



External Characters. A single fistula, about 40 millims. long and 

 19 broad at the broken base, and 12 broad at the vent-opening. 

 It has evidently been torn off from a larger specimen, as the oblique 

 fracture of the base of the tube shows. The walls are thickest at 

 the base, viz. about 7 millims., and taper gradually up to the edge 

 of the mouth, where they are of the thickness of cardboard. The 

 whole tube tapers in breadth from base to mouth ; but the iuterual 

 diameter remains the same throughout. It presents a slight con- 

 striction or neck about 7 millims. below the mouth, below which 

 point it has obscure longitudinal ridges, which become more marked 

 as they approach the base, and are there accompanied by slight pa- 

 pillary eminences. Besides the large mouth or vent, there is a lateral 

 opening, about 3 millims. in diameter, leading upwards into the cavity 

 of the tube. The colour is a dark brown throughout. The sur- 

 face is regularly covered with minute points, between which lie the 

 pores. Texture subelastic ; the interior of tube has a honeycombed 



