18 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



the third pair of ambulacral ossicles. In tenella each facet is higher than wide and 

 the combined pair about as broad as the height (in pusilla the combined pair is much 

 broader than high, and in rays of the same size actually much smaller). The disk of 

 tenella is unknown. 



The rudimentary scattered plates of the disk will at once separate this species 

 from fragilis, which, furthermore, does not have costae on the outer half of ray, has 

 regularly three actinostomial spinelets and two aboral furrow spinelets to each mouth 

 plate; in addition the first marginal plates of pusilla are slenderer, the outer end of 

 the combined marginal plates is broader, and the rays decidedly narrower and weaker 

 to disks of the same size. Putting it conversely, the disk of fragilis is proportionately 

 smaller. 



BRISINGELLA PANNYCHIA, new species 



Plate 8, Figure 4, 4a 



Diagnosis. — Resembling B. fragilis in having a long costal region with numerous, 

 rather widely spaced costae, in having the dorsal end of the first ambulacral plate less 

 than twice the length of the second, and in having both an adoral and aboral furrow 

 spinelet. Differing from B. fragilis in lacking entirely any trace of the secondary, 

 intercostal, calcareous, incomplete arches, in having coarser costal spinelets, and 

 in having conspicuously longer and less numerous abactinal disk spines. Rays 10; 

 r = 8mm.; rays incomplete. 



Description. — Disk of the usual BrisingeUa form, thin, with a beveled margin. 

 Spinelets about 0.5 to 0.6 mm. in length, spaced about the same amount, generally 

 solitary, but occasionally with two or three to a plate, very delicate and sharp, but 

 when incased in the usual membranous covering blunt and papilliform. They are 

 fully twice as long as the disk spinelets of B. fragilis and much less numerous. As 

 compared to B. pusilla, the disk spinelets of pannychia are more numerous and some- 

 what longer; they appear to be more like those of pusilla than like the minute close- 

 set spinelets of fragilis. There are relatively few tiny pedicellariae attached to the 

 basal portion of the spinelets. Interradial plate rather prominently convex but with 

 a more rounded surface than in pusilla; the plate is a little shorter and broader than 

 in either pusilla or fragilis. 



Rays represented only by basal parts, none complete; longest fragment with 19 

 costae; there are apparently many more. Costae slender, spaced 3 to 5 mm. and 

 bearing relatively few spaced, sharp spinelets about 0.75 mm. long. There is a 

 slender rather inconspicuous intercostal band of pedicellariae. The costae correspond 

 to every alternate adambulacral and there is a slender lateral spine on either side at 

 the base of each arch, as usual in this genus. When fully developed this spine is 

 equal to a little over three consecutive adambulacral plates in length. 



Adambulacral armature: One aboral furrow spinelet about as long as one-third 

 the length of the plate; an adoral spinelet about two-thirds the length of the plate 

 and spaced about half its own length from the adoral margin of plate; a slender sub- 

 ambulacral spine (none perfect). There is a syzygy between the first and second 

 adambulacral plates. The second ambulacral ossicle is about two-thirds the length 

 of first measured on summit of ridge. 



The mouth plates are in general form very similar to those of pusilla and fragilis; 

 they extend externally between the first adambulacrals of adjacent rays, these plates 



