MUSEUM OF COMPARATIVE ZOOLOGY. 333 



mentary under arm-plate ; under arm-plates nearly pentangular, but 

 there is a very short inner side, because the inner laterals do not meet on 

 the median line ; they are bounded without by a slight curve ; on the 

 sides by curves a little re-entering; the inner laterals are also somewhat 

 re-enteringly curved : length to breadth (5th plate) .5 : .4. Side arm- 

 plates quite large, and encroaching both above and below ; nearly meeting 

 above. Upper arm-plates rounded, with a peak within ; they do not cover 

 the whole upper surface, but on each side appear the side arm-plates ; 

 length to breadth (3d plate from disc) .5 : .5. Disk finely scaled above, 

 naked below ; scales rather larger towards middle of disk ; near its edge 

 there are about 140 to a square mm., all thin, and overlapping. Radial 

 shields narrow, broader without than within ; their sides overlapped by 

 the disk scales ; nearly, or quite, touching without; diverging a little 

 within ; separated near their outer ends by a single long scale, and, further 

 inward, by a bunch of the imbricated disk scales, length to breadth 1 : .3 ; 

 they vary somewhat, accordingly as they are more or less encroached on 

 by the disk scales. Just outside and below each of them is a small radial 

 scale. Arm-spines, near base of arm, five ; further out, four ; stout, 

 rounded, tapering to a point, swelled at the base ; the two upper ones 

 slightly longer and more slender ; lengths to that of under arm-plate (5th 

 joint) .5, .5, .4, .4, .4 : .5. Tentacle scales two, small, broader than long, 

 curved ; placed at right angles to each other, one on the lateral side o*f 

 the under arm-plate, the other on the outer edge of the side arm-plate. 



Color, in alcohol, disk greenish gray, arms yellowish. 



A single specimen, from 377 fathoms, south of Rebecca Channel. 



The specimen was somewhat injured, and therefore I wait better exam- 

 ples before separating the species from Amphiura, from which it differs by 

 its naked disk underneath, just as does Hemipholis. Otherwise, it be- 

 longs to the Amphiura group, in which arc found the well-known European 

 A. Chiajii and the Florida A. Stimpsonii. This group is commonly de- 

 scribed as having one mouth-papilla at the outer corner of the mouth-slit, 

 and another high up in the mouth-slit itself. As the term mouth-papilla is 

 understood, this description is not true. The papilla at the outer corner 

 of the mouth-slit is the tentacle scale of the second pair of mouth-tentacles ; 

 that within the mouth-slit is the tentacle scale of the first pair of mouth- 

 tentacles. The scale of the second pair of tentacles may easily be found in 

 such genera as Ophiocoma, but naturalists do not there speak of it, because 

 it is hidden by the continuous row of true mouth-papilla?. The group, 

 therefore, should not be spoken of as having six mouth-papillae, but as 

 having two mouth-papilhe at the apex of the angle, and one large scale to 

 each of the mouth-tentacles. Its species are, moreover, characterized by 

 the number of the arm-spines, which are rarely less than five and occa- 



