NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 235 



OPHIACANTHA LEUCOSTICTA, new species.o 



Disk 17 mm. in diameter; arms about 70 mm. long. Disk covered 

 with a thin, uncalcified skin, which appears to be speckled with both 

 black and white ; examination with a lens shows that the black spots 

 are due to organic tissue on the inner surface of the skin, while the 

 white spots are due to minute, elongated calcareous granules; these 

 granules are borne by plates which for the most part have a diameter 

 scarcely exceeding that of the granules, but around the radial shields 

 they are developed into ordinary overlapping scales. Radial shields 

 rather large, distinctly separated, the distal half exposed but bearing 

 on the outer margin one or more elongated granules. Upper arm 

 plates rounded, hexagonal, or elliptical, much wider than long, more 



FIG. 111. OPHIACANTHA LEUCOSTICTA. x 3. a, FROM ABOVE; ft, FROM BELOW; c, THREE ARM JOINTS 



NEAR MIDDLE OF ABM, SEEN FROM BELOW; d, SIDE VIEW OF TWO ARM JOINTS NEAR DISK. 



or less in contact with each other, at least on basal part of arm. 

 Interbrachial space below like disk above. Genital slits large. 

 Oral shields somewhat rhombic, twice as wide as long. Adoral plates 

 moderate, short and wide, hardly meeting within. Oral papillae 

 three on a side, broad, flat, rounded. Teeth very large and con- 

 spicuous. First under arm plate hexagonal, about as long as wide; 

 succeeding plates more or less octagonal and longer than broad, but 

 rapidly becoming hexagonal, tetragonal, or rounded and much wider 

 than long; the first two or three are in contact, but the succeed ing 

 plates appear to be separated by a depression; whether the side 

 arm plates meet in this depression, or whether it is a proximal pro- 



, signifying white-spotted, in reference to the appearance of the disk. 



