118 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 2. Aulascus, n. gen. 

 This genus only contains one species. 



Aulasciis johnstoni, n. sp. (PI. XXII. figs. 1-3). 



The loose and readily pliable tube-like fragments which are figured in PI. XXII. fig. 1 , 

 have a waU from 2 to 4 mm. in thickness, and were dredged in the southern part of the 

 Indian Ocean, about halfway between the Cape of Good Hope and the Kerguelen 

 Islands, at Station 145a (lat. 46° 41' S., long. 38° 10' E.), from a depth of 310 fathoms, 

 and a bottom of volcanic sand. AVhile the inferior portion of both tubes is entirely 

 destroyed, a simple, sharp, smooth margin occurs on the somewhat widened upper portion 

 of one of them. Both the outer and the inner surfaces are covered by a continuous thin 

 skin, through which irregularly scattered cavities of variable widths (up to 2 mm. in 

 diameter) may be seen. 



In the parenchyma the principalia consist of moderately large hexacts with rough 

 ends which run out gradually to a point, and of numerous straight or slightly bent diacts, 

 which occur partly in bundles and partly isolated, and are provided with a central 

 thickening and with rough ends running out gradually into points. While the hexacts 

 are usually disposed at right angles to the bounding surfaces, the diacts are for the most 

 part parallel to these or arranged obliquely in different directions. 



Between the principalia numerous irregularly scattered rosettes appear. Among 

 these discohexasters predominate, and each of their principal rays is divided into two or 

 three diverging straight terminals. The latter decrease in size towards the exterior, are 

 densely beset with numerous short hooks, and terminate in a small, slightly arched, 

 transverse disc which runs out into four or more prongs. In some cases the outer 

 extremities of the terminal rays are so delicate, and the terminal transverse disc so 

 small, that the latter can only be seen with high magnifying powers, and the whole rosette 

 resembles an oxyhexaster. 



The plumicomes (0'05 mm. in diameter), indicated in PL XXII. fig. 2, and figured in 

 fig. 6 from another sponge, occur here and there. The extremity of each of the moderatelj'^ 

 long, round, principal rays bears a tolerably thick, round, transverse disc, on the convex 

 outer side of which the fine terminal rays, which are bent in an S-shaped manner, arise in 

 concentric circles and together form a cup. 



The dermal skeleton is supported by moderately large pentact hypodermalia with 

 rough ends, which gradually run out to fine points. The abortive distal ray is some- 

 times indicated by a round tubercle. The dermal membrane itself contains the four 

 cruciate transverse rays of the hexact autodermal pimdi, in which the freely projecting 

 distal ray is beset with scaly prongs, like a fir cone, in its larger outer principal portion, 

 while the base remains naked (PI. XXII. fig. 3). The pole-like pointed proximal is 



