82 THE SPONGES. 



just described. Topsent (1901) likewise finds in his Eiireie alicei nicked 

 oxjdiacts, which he considers as a form of uncinate. The oblique char- 

 acter of the denticulations in the larger oxydiacts of H. lahyrinthica inevit- 

 ably suggests that they too are to be regarded as representing uncinates. 



Discohexasters, Fig, 3, Plate 11, are abundant in the parenchyma. 

 The principal rays are smooth, the terminals roughened and exceedingly 

 slender. A principal bears 3 or 4, rarely only 2 terminals. The buttons 

 at the ends of the terminal rays are minute. The principals are commonly 

 5 /u, long, the terminals 20 /x long, although somewhat smaller sizes are 

 present. 



Hexactinella ventilabrum Carter (sp. ?). 



1885. Hexactinella ventilabrum Carter, 1885, p. 397, Plate XIV., Figs. 1-10. 

 1887. Hexactinella ventilabrum Carter, Schulze, 1887, p. 331, Plate XCVI. 



Four fragmentary specimens from Stations 33S9, SJfiJf, 3406. 



These specimens include only the dictyonal framework, and the identi- 

 fication is therefore in a measure uncertain, although a direct comparison 

 with specimens of H. ventilabrum makes it probable that they belong to 

 this species. 



The largest piece is a plate about 120 mm. wide and 7-10 mm. thick. 

 The plate is comparatively smooth on one surface, but very uneven on 

 the opposite surface, owing to the development of irregular protuberances 

 and ridges, which for the most part are about 10 mm. high. The dictyo- 

 nal framework exhibits the reticulate plates, which are characteristic of 

 the genus. They curve toward both surfaces, and are made up of beams, 

 which are covered with very small, sharp microtubercles. Except at and 

 close to the surfaces of the sponge, where they are conspicuously thickened, 

 the beams have a thickness commonly in the neighborhood of 80 ft. The 

 meshes more frequently are irregular in shape, but in places are square or 

 rectangular. Selected and fairly typical meshes of this character measured 

 425 /x x 300 fx, 340 ^ x 250 /x, 250 /x x 250 /x. Much coarser meshes 



exist. The distance between the reticulate plates is about 2 mm. 



The framework is thus a coarse one. 



As in Schulze's specimens of 11. ventilahrum (and in other species of 

 Hexactinella also), there is a marked difference in the appearance of the 



