160 BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



AMPHIODIA PERIERCTA, new species.o 



Disk 14 mm. in diameter; arms about 150 mm. long or more, 

 probably. Disk distinctly pentagonal, with nearly straight sides, the 

 margin formed by a row of quite distinct scales, which may stand more 

 or less erect and be bluntly pointed. In the type, the interbrachial 

 spaces are so swollen, presumably with the reproductive cells, that they 

 project out far beyond this margin (see fig. 68a), while in a smaller 

 specimen (fig. 68d) drying has caused enough shrinkage so that the 

 disk margin is a little concave and the marginal scales are just below 

 the edge, beyond which they project in quite a conspicuous manner. 

 Disk covered by numerous irregular scales, the largest of which are 

 near the radial shields. Radial shields small, closely joined, at least 



FIG. 68. AMPHIODIA PERIERCTA. x 3.5. a, FROM ABOVE; b, FROM BELOW; c, SIDE VIEW OF THREE ARM 



JOINTS NEAR DISK; d, A MUCH YOUNGER SPECIMEN, FROM ABOVE, X 9. 



distally; they are broadly oval in the young specimen, but are twice 

 as long as wide in the type. Upper arm plates very wide, somewhat 

 tetragonal with more or less rounded ends, two or three times as wide 

 as long, broadly in contact throughout. Interbrachial spaces below, 

 very closely covered with fine scales, in marked contrast to the disk. 

 Oral shields small, somewhat pentagonal or triangular, with an inner 

 angle, and outer side curved, wider than long. Adoral plates not 

 conspicuous, wider without than within. Oral papillae three on a 

 side, thick, rounded and subequal. Genital slits large. First under 

 arm plate, small, much wider than long; succeeding plates squarish, 



, signify ing fenced round, in reference to the distinctly bounded disk. 



