84 



BULLETIN 76, UNITED STATES NATIONAL MUSEUM 

 Specimens of Ampherasler marianus examined 



Remarks. — This very distinct species combines in a curious manner the appear- 

 ance of Pedicellaster when viewed dorsally with that of Myxoderma when viewed 

 ventrally — but a Myxoderma with uniform monacanthid adambulacrals. 



If the unique specimen of Ampheraster liyperoncus (H. L. Clark) 30 is typical of the 

 species, it is sharply separated from marianus by having strictly biserial tube-feet, 

 even the ambulacral pores being biserial. I have examined this specimen which has 

 R 68 mm., r 7 mm. There are only two series of very large dorsolateral skeletal 

 meshes (four in all) which are clearly indicated by Clark's figure. The superomar- 

 ginal plates are very unusual in form. Instead of being regularly + form, the proximal 

 plates are Y-shaped, while the rest might be described as similar to two Y' s joined 

 by fusing the handles. (See PI. 32 fig. 4.) Interpolated among these is an occa- 

 sional Y-shaped plate. The superomarginals of liyperoncus are well spaced from the 

 inferomarginals, most of the intermarginal papular areas being broader than long. 



AMPHERASTER CHIROPLUS, new species 



Plate 31, Figures 3, 3a-3et; Plate 32, Figure 2; Plate 35, Figure 2; Plate 37, Figure 2 



Diagnosis. — Rays five. R 33 mm.; r 5 mm.; R = 6.6 r; breadth of ray at base, 

 6 mm. Disk small; rays slender, slightly swollen, gradually tapered; skin rather 

 thick; distally two series of large skeletal meshes on either side of the carinal plates; 

 proximally the biserial order is broken and there may be but one broad mesh; supero- 

 marginal plates three-lobed, forming a zigzag series; spinelets very small, rather 

 widely spaced; adambulacrals strictly monacanthid, the spines rather long and 

 slender, subequal to the slightly stouter inferomarginal spines; straight pedicellariae, 

 very large, spatulate, unguiculate, the shank constricted; crossed pedicellariae in 

 profile broader distally and blunter than in A. liyperoncus or A. atactus; tube-feet 

 quadriserial proximally. 



Description. — The abactinal skeleton consists, distally, of four longiseries of meshes 

 and proximally, irregularly of two or four. When there are only two each mesh 

 extends from the series of fairly regular four-lobed carinal plates to the superomar- 

 ginals The dorsolateral plates are generally regularly Y and A form, distally, form- 

 ing on either side a zigzag series; but on the proximal half of the ray they are not 

 regular. The superomarginal plates are usually the same shape as the distal dorso- 



» Pedicellaster hyperoncus H. L. Clark, Bull. Amer. Mus. Nat. Hist., vol. 32, art. 8, 1913, p. 201, pi. 44, figs. 3 and 4; station 

 5645 southwest of San Cristobal Bay, west coast of Lower California, 284 fathoms, bottom temperature, 44.6° T. 



