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



coronal plates, while in its general appearance, its colouring, and the sti'ucture of the 

 spines it approaches Astlienosoma tenue. Notmthstanding that there is but a single 

 adult specimen of this species, I have no hesitation in describing it as distinct. The 

 colour of the test in alcohol is yellowish, the spines of the same tint, Tvdth large violet 

 patches on the actinal surface. The special characters of Asthenoso'ma gracile are the 

 two irregular rows of small primary tubercles in the ambulacral area extending about 

 half-way to the abactinal system from the ambitus, and in the interambulacral areas the 

 coronal plates near the ambitus carrpng from three to four primary tubercles (PI. XVII. * 

 fig. 4) ; while further towards the abactinal region the number of large tubercles is gradually 

 reduced to one on every other plate. There are secondaries or miliaries loosely and 

 irregularly arranged on the narrow plates ; the interstices between the coronal plates of 

 both areas are much as they are in Asthenosoma hystrix, judging from the width of the 

 connecting membrane. On the actinal side the primary tubercles of the interambulacral 

 area form, as they do in Asthenosoma hystrix, two principal vertical rows extending from 

 the ambitus to the actinostome, the one adjoining the poriferous zone, the other in the 

 median line; the rest of the plate is occupied by from four to seven small secondaries 

 with a few miliaries arranged in irregular horizontal rows (PI. XVII.'' fig. 3). In the 

 ambulacral area the primary tubercles are small, arranged in an iiTcgular vertical row 

 nearer the median line, with secondaries and miliaries placed much as they are in the 

 interambulacral zone. The actinostome of the specimen figured natural size on 

 Plate XVII.'' fig. 1, measured 26 mm. in diameter, the abactinal system 16 mm. The 

 primary spines are short, slender, blunt at the extremity, diff"ering mainly in size from 

 the shorter and sharper secondaries and miliaries. On the actinal surface, however, the 

 spines of the actinal membrane are slightly curved and spathiform, and a few of the 

 primary spines are also curved, trumpet-shaped, flaring at the extremity. The abactinal 

 system (PL XVII." fig. 2) diffei's from that of Asthenosoma pellucidmn in having large 

 pointed genital plates extending into the median interambulacral s^aace and comparatively 

 small ocular plates, while the aljactinal system of Asthenosoma jyellucidum is remarkable 

 for the uniform size of the ocular and genital plates (PI. XVIII. fig. 6). 



Small specimens of Asthenosoma from Stations 184 and 219 are referred to this 

 species with considerable doubt. The largest of these young specimens differs more from 

 Asthenosoma gracile (figured on PI. XVII.'') than young specimens of corresponding 

 size differ from Asthenosoma j^^T-lucidutn. The arrangement of the tubercles on the 

 abactinal surface (PI. XII.* fig. 5) in a specimen measuring 24 mm. is such as would be 

 found in a species of Asthenosoma at any rate closely aUied to Astlienosoma gracile, 

 although the appearance of the actinal surface is more like that of a Phormosoma than 

 that of an Asthenosoma, and the size and position of the ocular plates (PL XIL* fig. 5) 

 is different from that of the oldest Asthenosoma gracile figured on Plate XVII." 



Dr Studer (Monatsber. Berlin Akad., 1876, p. 464) has described from Great Harbour, 



