SILICIOUS AND HORNY SPONGES WILSON. 349 



The spicules are in dense conical bouquets, which, however, inter- 

 mingle close to their apices and form a continuous furze, (b) The 

 middle stratum, (u. c. m.) is only the space between the superficial 

 and the inner stratum. It includes some scattered tylostyles, 300 

 by 8 [j, to GOO by 16 p. (c) The inner stratum is somewhat thicker 

 than the superficial one, and is not so compact. It is composed of 

 tylostyles radiating obliquely in all directions from points near 

 the choanosomal border. A vague grouping in brushes is percepti- 

 ble in some spots. A common size of spicule is about 600 by 16 y.. 

 The spicules as a class are certainly thicker and probably somewhat 

 longer than those of the superficial stratum. 



The cortex of the lower (convex) face is also made up of three 

 strata, (a) The superficial stratum is not very compact. It is 

 composed of obliquely radial tylostyles, not in brushes, many pro- 

 jecting slightly. The prevailing trend is from the center toward 

 the margin of the sponge, but there is no great regularity of ar- 

 rangement. The spicules range from 300 by 8 \i. to 600 by 16 yi. 

 (b) The middle stratum, (I. c. m.) is dense. It is composed of long 

 spicules, compactly grouped; these are tangential, becoming radial 

 at the margin. The stratum is thickest in the center of the sponge, 

 and peripherally is continued into the marginal fringe. The 

 spicules within the limits of the body range from about 1,600 by 

 IT [x to 4 mm. by 24 \).. The spicules of the fringe (fr. s.) range 

 up to 10 mm. by 24 [x. (c) The inner stratum is much like the super- 

 ficial one. The tylostyles, often about 600 by 16 \j., radiate obliquely 

 from the choanosomal margin toward the surface, in general trend- 

 ing toward the fringe border of the sponge. 



The occasional slender process borne by the convex face of the 

 sponge includes thickly packed tylostyles arranged lengthwise in the 

 process. 



The choanosome contains some, but not many, scattered tylostyles, 

 ranging from 300 by 12 \k to 900 by 16 pu. It is, further, crossed by the 

 ascending radial skeletal bundles (pi. 48, fig. 1. a.r.b.). These bun- 

 dles pass from the central part of the lower cortex to and through the 

 upper cortex. Some, perhaps all, surround oscular canals. The bun- 

 dles are made up of compactly grouped tylostyles, 1-2 mm. in length 

 and about 20 \l thick, placed lengthwise in the bundle. The bundles 

 expand above, the spicules of the expanded end projecting on the 

 upper surface of the sponge somewhat farther than the surrounding 

 cortical spicules. Thus each osculum is surrounded by a special, 

 although vaguely outlined, fringe of spicules. 



Holotype.— Cat. No. 21306, U.S.N.M. 



In T. hemisphericum Sars from the Arctic Ocean there are several 

 quite long oscular tubes borne on the convex face of the sponge 



