﻿sponges. kallmann. i2q 



Family POLYMASTIID/K. 



Genus Polymastia, Bowerbank. 



Polymastia craticia, sp. nov. 



(Plate xxii., fig. 3, and fig. 25.) 



Sponge depressed dome-shaped, sessile, with tljick- 

 ivalled digitiform iuhidar processes some of which are 

 provided with a single apical oscidum. Main skeleton 

 consisting of a fairly dense matrix of scattered spicules 

 and spicule bundles traversed vertically by fairly stout 

 distant fibres. The fibres lying immediately beneath the 

 cortex of the processes comprise an outer series of wavy 

 fibres running circumferentially and forming an elegant 

 wickerwork, and of an underlying series of equidistant 

 longitudinal fibres. The cortex consists of styli arranged 

 i)i a dense palisade. Spicules : — These are of three kinds, 

 viz., fusiform styli of two orders of size ivhich [par- 

 ticularly the larger) are scarcely distinguishable from 

 oxea, the larger occurring in the main skeleton, the 

 smaller in the cortex; and fusiform tylostyli which occur 

 along with the larger styli scattered through the ground 

 tissues. The first attain a size of 1200 x 22 ji ; the second, 

 330 .V 9 II : and the last, 200 x 5 u- 



The sponge is sub-circular in horizontal outline, broadest at 

 the base, with a convex upper surface from which numerous 

 longer or shorter stout digitiform processes arise. Of four 

 specimens, the two which differ most in their proportions are 

 respectively 55 x 80 x 50 mm., and 40 x 90 x 75 mm. in 

 aeight, length and breadth. These two also differ most in the 

 lengths of their processes, which in the former are never more 

 than 10 mm. long, in the latter usually between 15 and 30 mm. 

 The processes are usually tapered to a point and vary from 

 60 to 80 in number. When, as sometimes is the case, they 

 are cvlindrical and distally rounded, the osculum, if it occurs, 

 is situated on the summit of a small terminal papilla. 



The specimens are preserved in a dry state, and the follow- 

 ing remarks therefore apply to the sponge in that condition. 

 The surface is quite smooth to the touch but has a minutely 

 velvety appearance due to the slightly projecting points of the 

 densely crowded cortical spicules. Internally the sponge con- 

 sists of a dense, but rather soft and friable matrix traversed 

 verticallv by fibres about 250 }i in stoutness. The fibres are 

 composed solely of closely packed spicules of the largest kind, 

 which are fusiform styli closely resembling oxea ; the matrix 

 consists of a disorderly profusion of spicule-bundles and single 



