48 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



Ambulacral furrow broad; tube-feet crowded, four-ranked, except on the outermost 

 attenuate portion of the ray. 



Mouth plates small but brisingoid in shape— that is, with the actinostomial 

 margin broadened fanwise — and bearing two short marginal spines, loaded with 

 pedicellariae. Suboral spines two, tapering, bluntly pointed, in a longitudinal series. 



Madreporic body small, convex, situated near entrance to interbrachial sulcus 

 12 mm. from center. Anal aperture considerably to one side of center. 



Color in life, buffy "salmon" pink. 



Anatomical notes. — Specimen from station 4517. The stomach is a depressed 

 subspherical sac filling the coelom of the disk but not extending into the rays. There 

 is no separate dorsal stomach, nor even a fold of the wall to indicate a dorsal division 

 of the cavity. The hepatic coeca are rather thick and extend about one-third the 

 length of the ray; their lateral branches have very numerous, crowded, short irreg- 

 ular lobules. The two coeca open independently side by side into each radial area 

 of the stomach. Sometimes the first branch of each coecum opens independently, 

 just dorsad to the main tube, into the stomach. The hepatic coeca and the gonads 

 completely fill up the proximal third of the coelom of the ray. From the middle of the 

 dorsal side of the stomach departs the extremely short intestine into which open two 

 digitiform coeca (one forked) about 10 mm. long. These two really unite into a 

 common base before joining the intestine. The dorsal wall of the stomach is thrown 

 into folds, which from the inside consist of radiating, ramified grooves separated by 

 thickened glandular spaces; from the outside these grooves are raised, and the glan- 

 dular parts depressed. Gonads massive, branched, two to each way. The gonoduct 

 is attached to the wall close to the outer end of the first enlarged superambulacral but- 

 tress (see below) and on a level with the upper border of the inferomarginal plates. 



Interbrachial septum narrow, thin, and membranous; the attached outer inter- 

 brachial border is in the angle formed by two buttresses (which join the conspicuous 

 knob-like proximal end of the ambulacral ridge to the interbrachial angle of the body 

 wall). These buttresses (pi. 14, fig. 5) are really very much enlarged superambulac- 

 ral ossicles, are compressed, and each consists of usually two large and several small 

 pieces closely united. In each interradius a pair of these stays forms an acute angle 

 inclosing the interbrachial septum, and (on either side of the base of the latter) a 

 tube-foot (two in all). The superambulacral ossicles are conspicuous on the proxi- 

 imal part of the ray and are usually in pairs to each (lowest) actinolateral plate (one 

 to each ambulacral plate). No Polian vesicles; Tiedmann's bodies small, spaced; 

 ampullae single; when deflated they have a long terminally curved division toward 

 the ambulacral ridge, and a short outer incipient lobe. Tube-feet large with a very 

 small button or disk. 



Young. — The smallest specimen of the northern race measures R 58 mm., r 9 

 mm., R = 6.4 r; breadth of ray at the base, 11 mm. The abactinal and marginal spines 

 are from 2 to 3.5 mm. long and hence relatively more conspicuous than in large speci- 

 mens. The abactinal papular areas contain one or two papulae; the adradial spines 

 are relatively small; pedicellariae of abactinal surface few and small; the third actino- 

 lateral series of plates just starting at the base of ray; the first does not reach the end 

 of ray by 10 mm., and the second series stops nearly 20 mm. short of the end. The 



