518 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



plate joined for their whole length to the respective plates of adja- 

 cent ray; thus there are 4 closely joined plates in each interradius ; a 

 nonmuscular symphysis or syzygy between first and second adam- 

 bulacral plates and between the dorsal part of the second and third 

 ambulacral plates, as in Brisinga. 



Remarks. — The two species which are included in this genus are in 

 most respects closely similar to Brisinga, s. s., except for the regular 

 circle of papulae near the margin of the disk, there being 2 papu- 

 lae for each radius. The first pair of adambulacral plates is more 

 closely joined than in true Brisinga, judging by the figure of B. 

 endecacnemos Asbj0rnsen, given by G. O. Sars (1875, pi. T, figs. 8 

 and 9.), and the condition of these plates in B. trachydisca. The 

 outer ends of the plates tend to radiate apart somewhat, and in the 

 second species the united first pair of marginals slips down between 

 them. 



KEY TO THE SPECIES OF BRISINGEXES HEREIN DESCRIBED. 



o\ Conspicuous costae 25 to 30, occupying proximal fifth of ray ; peclicellariae 

 larger, the proximal serrate edge of each blade inconspicuous, semi- 

 circular ; articular surface of proximal ambulacral ossicles smaller ; rays 

 16 mimica, p. 518 



a'. Conspicuous costae about 40, occupying proximal fourth of ray ; pedicellariae 

 smaller, with the proximal serrate edge of each blade relatively larger in 

 proportion to total length of blade and different in form ; articular surface 

 of proximal ambulacral ossicles larger, the pair being 1.5 times higher than 

 broad; rays 14 anchista, p. 521 



BRISINGENES MIMICA (Fisher). 



Plate 147, figs. 3-5 ; plate 149, fig. 4 ; plate 152, figs. 4, 4a-d. 



Brisinga mimica Fisher, 1916&, p. 32. 

 Brisingenes mimica Fisher, 1917/, p. 427. 



Diagnosis. — Rays 16. Costae numerous (25 to 30), closely placed, 

 prominent, irregular, with relatively coarse spinelets, without inter- 

 vening bands of pedicellariae ; costae confined to basal fifth of ray, 

 beyond which for an equal distance are about 15 very inconspicuous 

 ridges composed of small plates, but carrying a fairly heavy felting 

 of pedicellariae; disk large, with isolated delicate spinelets not in 

 groups; adambulacral plates proximally wider than long and 

 crowded in appearance ; armature typically 1 aboral furrow spinelet, 

 1 aboral actinal spinule and 1 longer adoral actinal spine (equal- 

 ing 2 plates in length), and 1 major spine about 3 plates in length. 

 Rays slender, very long; R=385 mm., r=:19 mm. 



Description. — Disk large, with rounded borders. The small, 

 granuliform abactinal plates, with solitary, delicate spinelets, about 

 0.75 mm. long and spaced about their own length, give the abacti- 

 nal surface of disk a very finely hirsute or downy appearance. 



