82 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



forms a slight ridge. The dorsolateral area is broad. In fully grown specimens the 

 plates are so arranged that there is one longiseries of broad papular areas, or meshes, 

 adjacent to the carinals and another adjacent to the superomarginals, while between 

 the two there is a double row of much smaller irregular or lozenge-shaped areas, the 

 meshes of each series of the four dorsolateral series alternating with those of adjacent 

 series. (PI. 32, fig. 1.) Ludwig 29 (pi. 33, fig. 195) indicates only three dorsolateral 

 series of papular areas, but two of his cotypes which I have clearly show four at the 

 base of ray (R 40 mm.). The dorsolateral plates are three or four lobed and are a 

 little smaller than the carinals. The latter are a trifle smaller than the four-lobed 

 superomarginals, which are strongly imbricated into a regular series, fairly low on 

 the side of the ray. The distal superomarginals although four-lobed are "warped" 

 out of shape so that the dorsal lobe is advanced further distad than the ventral, a 

 feature often exaggerated in other species of this genus. The proximal plates do 

 not as a rule show this very markedly. (PI. 32, figs. 1, la.) The inferomarginals, 

 also strongly imbricated, are a little larger than the superomarginals and are jux- 

 taposed to the adambulacrals. There are a few inconspicuous intermarginal ossicles 

 at the base of ray. 



In the interbrachial angle the second superomarginal is conspicuously enlarged 

 and is firmly joined to the second enlarged plate of the adjacent ray. The lower end 

 of this pair of interbrachial plates overlaps a pair of similarly enlarged inferomarginals. 

 The four constitute a very firm interbrachial skeleton. The joined pair of first 

 superomarginals continue the interbrachial skeleton upward to the primary interradial 

 plate of the disk. 



The plates of ray have mostly one spine each. By reason of the open skeleton 

 the spines are well spaced, and are short, stout, tapered, pointed, rough, and in length 

 usually about half the greatest diameter of the plate. The superomarginal spines 

 are scarcely different from the abactinal but are sometimes much blunter. In the 

 largest specimen (station 2896) the abactinal spines are, relative to the plate, shorter 

 than in small examples, and measure about 0.7 to 0.9 mm. long. The acicular, 

 pointed, outwardly directed, inferomarginal spines stand on a prominent convexity 

 of the plate and are as long as 2 or 2.5 inferomarginal plates, slender, but robust, 

 in smaller specimens, heavier and slightly flattened in the large ones. A few of the 

 proximal plates in the largest specimens may carry a second smaller spine above the 

 first. 



The large adradial papular areas contain five or six papulae proximally; the 

 smaller intermediate, dorsolateral areas have about three; the supramarginal four 

 or five, the intermarginal, four to six. 



The adambulacral plates are small (30 to 32 corresponding to the first 10 spinif- 

 erous inferomarginals) and carry a slender, acicular spine equal to the length of 

 about four consecutive plates. Behind the mouth plates the first pair of adambula- 

 cral plates is separated by a muscualr symphysis, fairly wide in small specimens, 

 gradually narrowing with age, until in the largest specimen (station 2876) the plates 

 touch by the corners nearest the mouth plates. In one of Ludwig's cotypes (station 

 3425), R 40 mm., the plates are separated by a space as wide as the length of the first 

 adambulacral. In a slightly smaller specimen from station 2980 (southern California) 



".Mem. Mus. Comp. Z08I., vol. 32, 1905. 



