488 THE VOYAGE 0¥ ELMS. CHALLENGER. 



from the adoral point of the united mouth-plates, which becomes in consequence rather 

 conspicuous. Immediately behind, or aboral to the mouth-spines proper, is a single 

 superficial or secondary mouth-spine, smaller than the long mouth-spines. The three 

 mouth-spines of each plate are webbed together by a semitransparent membrane deeply 

 indented between ; and the secondary spine is united to the innermost spine by a cuii- 

 tinuation of the web. The long innermost spines are directed towards the centre of the 

 mouth, where they almost meet, the other spines radiating slightly outward from this. 

 The first, or most adoral, comb-series forms a widely expanded semicircular fan, the web 

 being continued and attached to the prominent aboral peak of the mouth-plates. 



The actino-lateral spines are robust, but short ; the character of the fringe is destroyed, 

 but probably was more or less distinct along the rays ; the spines do not reach to the 

 margin in the interbrachial arc, but are merged in the membrane of the actinal floor. 

 The margins of the rays and disk are well-rounded and regularly covered with the intra- 

 paxillar tissue continuous from the disk ; indeed the greater part of the actinal portion of 

 the interradial space has the paxillate character of the abactinal surface. 



Locality. — Station 299. Off the western coast of South America, between Valparaiso 

 and the Island of Juan Fernandez. December 14, 1875. Lat. 33° 31' 0" S., long. 74° 

 43' 0" W. Depth 2160 fathoms. Blue mud. Bottom temperature 35° - 2 Fahr. ; surface 

 temperature 62° "0 Fahr. 



Genus Calyptraster, Sladen. 

 Calyptraster, Sladen, Journ. Linn. Soc. Lond. (Zool), 1882, vol. xvi. p. 207. 



Form depressed. Marginal contour pentagonal. Abactinal area plane. Actinal area 

 convex. 



Supradorsal membrane very delicate, perfectly transparent. No muscular fibrous 

 bands. Spiracula present. No spicules. Paxillae with short, robust spinelets (five or six in 

 the type species), usually flaring at the extremity, crown widely expanded, not protruding 

 through, or even elevating the membrane, simply supporting it. 



Adambulacral armature forming transverse combs of spines ; the spinelets beino- 

 perpendicular in position, and webbed together. Segmental apertures present. Aperture 

 papilla? not free, opening laterally only. 



Mouth-plates with two or three pairs of superficial or secondary mouth-spines on the 

 actinal surface of the plates. Mouth-spines proper two, or occasionally three. 



Actinodateral spines merged in the actinal floor. No independent lateral fringe. 



Remarks. — This genus is established for the reception of a very elegant little form 

 which presents certain resemblances to Ilymenaster and also to Pteraster. It resembles 

 Ilymenaster in the absence of a marginal fringe and in the merging of the actino-lateral 

 spines in the actinal floor, and resembles Pteraster in having the armature of the adam- 



