42 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



in line with it. Outside of this is a slender spinelet similar to that of the prominent 

 plates and in line with it. 



Ambulacral furrow narrow; tube-feet rather crowded, at base of ray arranged in 

 two zigzag (or four) series, but in two series on outer half of ray. Tube-feet rather 

 slender, with a small sucking disk. 



Mouth plates very short, pretty well hidden on account of the upward bend of 

 the base of arms which carries the furrow dorsad. There are two sharp slender suboral 

 spiues and two spines at the narrow mouth of the furrow. One extends about halfway 

 across and bears several pedicellariae; another much shorter, also bearing one or two 

 small pedicellariae, extends over the actinostome. 



Madreporic body, 2.75 mm. in diameter, is convex, and its center is 7 mm. from 

 the center of disk. 



Anatomical notes. — The single stomach occupies the entire disk and sends a 

 short rounded lobe into each ray. From the dorsal surface of this diverticulum 

 (which is as broad as the inside of the ray) two hepatic coeca arise close together and 

 extend three-fourths the length of ray. From the sides of the central tube branch 

 off, in regular pinnate fashion, numerous small lobulated saccules, the whole gland 

 being narrow to conform to the tenuity of the coelom. The inner surface of the 

 stomach is very finely wrinkled and the walls are thrown into shallow folds. No 

 dorsal stomach. Into the tiny intestine empties a conspicuous coecum, consisting 

 in the specimen examined of two slender branches, one 15 mm. long, the other 3 mm. 

 The large branch, tubular in form, lies on the dorsal part of one ray. The gonads 

 are two to each ray, and open upon the side of the ray about 4 mm. from the inter- 

 radial angle. The gonads consist of a single axis from which depart numerous lob- 

 ulated branches. Interbrachial septum very small, rudimentary, membranous. 

 Ampullae single, but distal end expanded, and if not inflated would appear to be 

 somewhat fan-shaped. No Polian vesicles. No trace of superambulacral plates. 



Young. — The smallest specimen, from station 4400, has R 10 mm., and r 2.25 

 mm. It would be impossible to identify this correctly if it were unaccompanied by 

 adults. The rays are already very slender, about 2 mm. in diameter at the base. 

 There are present the carinal series, the beginning of the adradial series, the supero 

 and infero marginal series, but no actinolateral plates. Except for the adradials, 

 these and the large disk plates bear a relatively long central sharp spine, stoutest on 

 the carinal series, and a few delicate spinelets. There are a very few relatively large 

 pedicellariae, which, like the spines, are larger in proportion to the size of the plates 

 than in the adult. There is one papula to each area. The adambulacral plates do 

 not show any differentiations, there being a transverse series of three very delicate, 

 long, sharp spines. Tube-feet in two series. The mouth plates are relatively large, 

 not sunken, and separate entirely the first adambulacral plates of adjacent rays. 

 (In the adult three pairs of adjacent adambulacral plates meet by their outer ends on 

 the interradial line back of the mouth plates.) Like the adambulacrals, the mouth 

 plates have a single series of three sharp spines, that at the inner end of the plates 

 being quite small. The terminal plate is relatively prominent and bears six promi- 

 nent sharp spines, four horizontally directed (two from end, and one on each side) 

 and two on the ventral surface. From above the proximal end of the plate is notched 

 or emarginate for about half its length. The distal end is rounded. This tiny star 



