16 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



A nearer relative than tenella is Brisingella jragHis (Fisher) of the Hawaiian 

 Islands, which is the type of the genus. This species is rather variable in regard to the 

 adambulacral armature and the relative size of the secondary costae between the pri- 

 mary ridges. But it differs from exilis in having on the proximal adambulacral plates 

 an aboral furrow spinelet and also sometimes two or even three adoral furrow spine- 

 lets; the genital area is longer than in exilis (6 to 8 r from base of ray) and the costae 

 more numerous; the disk plates bear usually a single very smaU sharp spinelet; 

 the interradial plate is subcarinate; the first marginal is shorter in proportion to its 

 breadth at the inner end; the upper end of the second ambulacral ossicle is more than 

 half that of the first; there are regularly three actinostomial spinelets, and two 

 aboral furrow spinelets standing in a diagonal line with the suboral spinule. 



BRISINGELLA PUSILLA Fisher 



Plate 2, Figures 1, lo-l/; Plate 8, Figures 3, 3a, 36 

 Brisingella pusilla Fisher, Ann. and Mag. Nat. Hist., ser. 8, vol. 20, 1917, p. 427. 



Diagnosis.— Rays 10. R 165 + mm. ; r 8 mm., R = 20 + r; thickness of disk, 2.5 

 mm.; breadth of ray at base, 4 mm. Similar in general appearance to B. exilis, 

 having thin disk and deciduous, slender, flexible rays, thin delicate abactinal integu- 

 ment, and very fragile spines. Differing from B. exilis in having 25 to 30 costae 

 which extend at least three-fourths length of ray; comparatively few, widely spaced, 

 embryonic abactinal disk plates, bearing one, or occasionally two, small spinelets; 

 a narrower, keeled, interradial plate; second ambulacral ossicle more than half as 

 long as the first, measured on the summit of the ridge; furrow spinelet confined to 

 first few adambulacral plates (first 3 to 14). 



Description. — Abactinal integument of disk very thin and translucent. Abactinal 

 plates few, very small, and widely spaced, each with one, or sometimes two, very 

 small sharp spinelets, some of which bear a minute pedicellaria at the base. The 

 plates can only be seen when the integument is dried. They are irregular in form, 

 0.1 to 0.5 mm. in diameter and unevenly scattered, there being sometimes so much 

 as 2 mm. between plates. About 20 to 35 may be counted across the disk between the 

 borders of the actinostome. Madreporic body prominent, convex, on the border of 

 disk, with a number (five or more) of closely fitted plates on its adcentral side. These 

 combined are about as large as the madreporite. Interradial plate narrow, promi- 

 nently keeled, the upper end angular, the lower end truncate or slightly angular. 

 It is narrower than that of exilis and the surface is convex or keeled instead of being 

 more or less plane, with typically a longitudinal groove. 



Rays very deciduous, slender, with an attenuate, flexible, distal portion. Abact- 

 inal membrane very thin, devoid of intercostal spinelets or prickles. Costae delicate, 

 rather widely spaced (opposite alternate adambulacral plates), and composed of 

 slender, elongate, overlapping ossicles which bear each a conical sharp spinelet. On 

 the proximal part of the genital inflation the ridges are bent distally as a rule, and 

 are more or less irregular throughout the long costal region, which extends much 

 beyond the genital area proper, or fully three-fourths the length of ray. There are 25 

 to 30 costs, the distal ones being very inconspicuous and difficult to determine unless 

 the specimen is dry. There is a band of pedicellariae between each pair of costae, and 



