Verrill, JSTotes on Radiata. 575 



large, rounded and polygonal plates, joined by their edges, so as to 

 leave variously shaped spaces between, with their surface roughened 

 by minute, granule-like prominences and covered with a thin mem- 

 branous skin, which allows the roughness of the plates to show 

 through it. The median dorsal plates on each ray are stout, rather 

 rhomboidal, with the angles produced and rounded and the center 

 tubercular; they bear a row of eight to twelve, stout, elevated, blunt 

 spines, one to each plate. The sides of the rays near the base are 

 foi-med by about four series of plates ; in the two intermediate rows 

 rounded ; in the upper and lower ones with lateral prolongations, 

 which articulate with the dorsal and marginal plates in such a way as 

 to leave rather large, transverse, oblong openings between ; toward 

 the end of the rays the plates become more regular and uniform, 

 mostly polygonal, and more closely united, except that there are still 

 larger openings next to the marginal plates, forming a regular series. 

 Marginal plates stout, prominent, projecting laterally, and rounded 

 on the outer side, much broader than high, forming a single row, with 

 the plates placed alternately a little above and below the median line, 

 about 12 to 16 on each side of the ray, each one bearing a stout, elon- 

 gated, conical spine. Plates of the lower side rounded and subpolyg- 

 ona1, unequal, some of them bearing a very small central tubercle, 

 mostly closely united, so as to leave only small pores between. Each 

 interambulacral plate bears an outer, stout, oblong, blunt spine, com- 

 pressed or wedge-shaped at the tip, and an inner group of four or five 

 slender ones, of which the lateral are very short and the two middle 

 ones considerably longest, all connected together by a thin web. On 

 each margin of the mouth there is :i group of five to eight, rather 

 slender, subequal, obtuse spines, connected together by a Aveb. Near 

 the margin of the disk and rays, above and below, there are many 

 rather large pedicellariffi, oblong or subcylindrical in form, obtuse at 

 the tips. The dried specimens are light red above, yello^Wsh belo«'. 



The largest specimen is I'ijO inches from center to edge of disk; 

 2*75 to tip of rays; breadth of rays at base 1 to 1-25; length of 

 largest spines '20 to '22 ; diameter at base, about '08. 



A smaller one has the radius of disk "68 of an inch; of rays I'oO; 

 length of dorsal and marginal spines -10 to "12; diameter -05 or -06; 

 diameter of upper and loAver plates -05 to -10, mostly about "OS. 



Mithrodia Bradley! Ven-iU, (p. 288). 



From La Paz there are two dry specimens of this species. The 

 smaller and more perfect one is 3'50 inches from the center to the tips 

 of the rays; -50 to the edge of the disk; length of largest spines -lo; 



