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



are beset with numerous, somewhat recurved, thin, pointed barhs, wliich surround the 

 ray in irregular disposition (Pi. LX. fig. 5). 



The dermal skeleton is formed of medium-sized oxypentacts, with comparatively long 

 straight rays, which are, throughout their whole length, somewhat thickly beset witli 

 small pointed spines. The very ends of the four tangential rays are blunt and conical, 

 while the proximal ray usually runs more gradually to a point. In the position of the 

 undeveloped (sixth) distal radial ray, a rounded tubercle sometimes occurs. The equally 

 large gastralia exhibit the same structure and similar disposition (PI. LX. fig. 3). 



Several fragments of a connected skeletal framework, belonging to the same species, 

 were also trawled between the Marion and Crozets Islands (Station 147, lat. 4G° 16' S., 

 long. 48° 27' E.), at a depth of 1600 fathoms, and a Diatom ooze ground. The com- 

 pletely macerated skeleton contained no trace of soft tissue or of isolated spicules. 



Genus 11. Euryplegma, n, gen. 

 This genus contains only the one species Euryplegma auriculare. 



JEuryplegma auriculare, n. sp. (PI. GIL). 



Off Eaoul or Sunday Islands, to the north-east of New Zealand (Station 170a, 

 lat. 29° 45' S., long. 178° 11' W.), from a depth of 630 fathoms, and a volcanic mud ground, 

 two specimens of a plate-shaped Hexactinellid were trawled. They were, however, partly 

 macerated and only fragmentary. The best preserved but broken specimen has the form 

 of a semi-involute ear-shaped plate (PL GIL fig. 1 ). It measures 1 7 cm. in height, and 

 6 to 7 cm. in breadth. The macerated skeletal fragment of the other specimen forms a 

 semitubular stalk or basal portion 2 cm. in diameter, and this is continued on into a 

 closed plate 3 to 5 mm. in thickness, which forms the lower portion of a shallow funnel 

 (PL GIL fig. 2). The upper portion is unfortunately broken off. 



The convex outer surface of the involute ear-shaped specimen (3 to 5 mm. in thick- 

 ness) seems comparatively smooth, but is penetrated by numerous long oval holes which 

 lead into the runnels and ducts of the afferent canal system (PL CII. fig. 1). Near the 

 upper end several of these cavities are covered by a membranous continuation of the 

 thin sieve-like perforated dermal membrane (PL GIL fig. 3). The concave internal 

 surface is very rough and uneven in comparison with the outer surface. In the upj^er 

 portion there is a distinct system of longitudinal ridges with interjacent furrows about 

 2 mm. in breadth. Somewhat further down they are covered by transverse, arc-like, 

 broad flat zones, so that transverse ridges 4 to 5 mm. in breadth cross at right angles 

 over the deeper longitudinal ridges, and project into the interior. Still further down 

 transverse arcs exhibit knots or cushion-like elevations about 3 mm. in diameter, and 



