220 NATURAL HISTORY BULLETIN. 



Radials barely visible at the outer part; facing outward. Rays 

 spreading almost horizontal, connected by perisome extending 

 clown to the radials. First and second priinibrachs united by 

 articulation. Secundibrachs (distichals) 4, — the third and 

 fourth united by syzygy. Rays dividing two or three times; 

 in the latter case there are generally 3 — exceptionally 2 or 1 

 — tertibrachs (palmars) below the last bifurcation, the axillary 

 and the next one below it constituting a syzygial pair. In 

 the ultimate arm divisions there is a syzygial union between 

 the second and third brachials; the next syzygy is at about the 

 twelfth or thirteenth brachial; and beyond that they occur at 

 intervals of about 4 or 5 brachials. Pinnules occur on the 

 second secundibrach on the outer side of the ray, on the first 

 brachial above the axillary secundibrach, and on the first 

 brachial of the ultimate arm-division on the outer side; beyond 

 this they occur on every brachial at alternate sides, not count- 

 ing the hypozygal. Treating the form as primitively 10- 

 armed, and counting the arm-branches as occupying the places 

 of pinnules, the succession would be on secundibrachs 2, 4, 5, 

 7, 8. Proximal portion of first pinnules fixed by perisome. 

 Arms 4, 5, or 6 to the ray, — giving 23 and 26 arms respect- 

 ively in the two specimens found. They are about 13 cm. 

 long, slender, and extremely brittle; the first six or seven 

 brachials wider than long, quadrangular, with parallel trans- 

 verse articulations; beyond that becoming strongly triangular 

 with zig-zag articulations, and the relative length increasing. 

 Oral pinnules about 22 mm. long; those at the middle of the 

 arm 12 mm.; they are stout at the base, tapering rapidly, and 

 slender, distally the lower ones have the combing characteristic 

 of the genus. Ambulacral grooves lined with alternating cov- 

 ering plates on the arms and pinnules, and to some extent on 

 the disk. Disk naked, without sign of other plates or spicules, 

 and finely granular; mouth marginal and radial; anus central 

 and protuberant, composed of longitudinal spicules. 

 Locality: Dry Tortugas, Florida. Depth, three feet. 



This species is apparently quite distinct from any hereto- 



