OPHIURANS OF UNITED STATES NATIONAL MUSEUM. 137 



Family ASTROCHEMID^. 



ASTROCHEMA ELONGATUM, new species. 

 Plate 17, figs. 1-3; plate 18, fig. 8. 



Fish Hawk station 7280. Feb. 14, 1902. Lat. 24 17' 05" N.; long. 81 58' 

 25" W.; 132 fathoms; sand; temp. 52 F. Three specimens. 



Type. Cat. No. 32309, U.S.N.M. 



The jar containing the three specimens was, unfortunately, badly corked and 

 consequently reached me completely dried, as well as a few Ophiomitra valida, which 

 accompanied them; the result is that the arms, which by the way are very long, 

 are fixed up in the position which they occupied when in alcohol, and as they are 

 strongly twisted up, it is rather difficult to form an accurate idea of their real length. 



In the largest specimen, the diameter of the disk reaches 1 1 mm. from the end 

 of a radial rib to the middle of the opposite interradius ; the length of the arms must 

 have been about 30 centimeters. The other two samples are smaller, and the 

 diameters of their disks, respectively, measure 8 and 7 mm. 



The disk is strongly excavated in the interradial spaces and is very thick. The 

 upper face is convex, more or less depressed in the central region; the under face 

 is plane. The upper face has 10 protruding and much elongated radial ribs which 

 all meet toward the center of the disk; the two ribs of each pair always remain 

 somewhat separated from each other by a more or less broad space. These ribs are 

 very narrow and they preserve the same width over almost all their length, except 

 at the proximal end which grows rapidly thinner and at the distal end which, on the 

 contrary, is widened. These ribs are noticeable not only from their being very 

 protruding, but also from their white color which shows off on the rest of the disk, 

 the tegument of which is dark brown. They are beset with thick granules which 

 are very dense and contiguous, and among which some bigger ones are noticeable 

 which are separated by other much smaller ones; all these granules, even the 

 largest ones, are rounded. The radial and interradial spaces of the upper face are 

 covered by a tegument carrying granules which always remain smaller than those 

 of the radial ribs; these granules also are unequal, but they are less dense than on 

 the ribs. When reaching the margin of the disk, and also in the vicinity of the 

 distal end of the radial ribs, these granules become a little coarser and they pro- 

 gressively extend over to the granules of the upper face of the arms. 



The lateral faces of the disk, which are obliquely directed inwardly, meet the 

 upper face by a rather conspicuous angle ; they show the same coloring as the radial 

 and interradial spaces of the said face, and they are covered with similar granules. 

 The two genital slits of each interradial space are obliquely directed inward, and 

 converge toward the ventral face; they are elongated, rather wide, and preserve 

 the same width over their whole length, which reaches 3 mm. 



The under face of the disk is covered with minute granules, of a uniform size, 

 and separated from each other; these granules become a little stronger toward the 

 margin of the disk in the interradial spaces; on the contrary, in the radial parts 

 they succeed the analogous but somewhat smaller granules existing on the under 

 face of the arms. 



