ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FISHER 81 



and key because in dried specimens it is fairly easy to recognize. It must be used 

 with caution because since the tendency to warping of distal superomarginals is 

 apparent even in Tarsaster (and in other genera less closely related), the effect may 

 be due to growth strains. In chiroplus, however, the curiously formed four-lobed 

 plates are, at least sometimes, due to the fusion of two three-lobed ones. 



The conspicuous, unguiculate, often spatulate hand-shaped pedicellariae and the 

 enlarged interbrachial marginals of Ampheraster will serve as differentiating char- 

 acters, while the absence of an accessory inferomarginal spinule will further aid in 

 placing the species. 



KEY TO THE KNOWN SPECIES OF AMPHEKASTER 



a 1 . Adambulacral plates monacanthid to tip of ray. 



6 1 . SuperomargiDal plates normally four-lobed, + form (sometimes slightly warped), imbricated 

 in a regular series; dorsolateral skeleton with three or four series of meshes on either 



side of the carinal plates; tube-feet strongly quadriserial marianus (Ludwig). 



b 2 . Superomarginals largely three-lobed (or, if four-lobed, warped), imbricated in a zigzag series; 

 dorsolateral skeleton with two series of meshes on either side of the carinal plates. 

 c'. Tube-feet biserial throughout the ray, the ambulacral pores broadly elliptical, in straight 

 series; straight pedicellariae much compressed, large, unguiculate; mouth plates 



broad hyperoncus (Clark). 



c 2 . Tube-feet quadriserial on proximal half of ray, the ambulacral pores narrowly elliptical, 

 in zigzag series proximally; straight pedicellariae very large, broadly spatulate, with 



three or four curved, interlocking tines; mouth plates narrow chiroplus Fisher. 



a'. Distal adambulacral plates diplacanthid; tube-feet quadriserial; marginal skeleton somewhat 

 irregular, the superomarginals usually three-lobed, sometimes warped four-lobed; straight 

 pedicellariae broadly spatulate with three or four coarse, curved, interlocking tines, spinelets 

 conical, rough; dorsolateral skeleton with two series of skeletal meshes distally on either 

 side of the carinal plates; proximally there may be three or four irregular meshes between 



carinals and superomarginals but not in serial order ataclus Fisher. 



a'. The first six or eight adambulacral plates diplacanthid, the rest monacanthid; abactinal and 

 marginal spinelets, one to a plate, slender, tapered; dorsolateral skeletal meshes in three 

 longiseries proximally, two distally; superomarginals four-lobed more or less warped; 

 tube-feet strictly biserial throughout the ray; oral plates with one actinostomial and two 

 suboral spines; unguiculate straight pedicellariae (0.8 or 0.9 mm. long) on furrow margin 

 and oral plates; (400 fathoms, Straits of Macassar) distichopus (Fisher). 



AMPHEKASTER MARIANUS (Ladwig) 



Plate 31, Figure 2, 2a— 2/; Plate 32, Figures 1, la; Plate 35, Figure 1; Plate 38, Figures 1, 2, 3, 4. 

 Sporasterias mariana Ludwig, Mem. Mus. Comp. Zool., vol. 32, 1905, p. 231, pi. 33, figs. 



194-198. 

 Ampheraster marianus Fisher, Ann. and Mag. Nat. Hist., ser. 9, vol. 12, 1923, p. 253. 



Diagnosis.— Rays five. R 76 mm.; r 10 mm.; R = 7.6 r; breadth of ray at base 

 10 mm. (slightly inflated beyond base); rays very gradually tapered to a pointed 

 extremity; abactinal surface arched, actinal surface subplane, accentuated by the 

 single series of acicular, usually horizontally directed inferomarginal spines; skeleton 

 and spines covered by a thickish skin; skeleton open; about eight longitudinal series 

 of abactinal meshes, subdivided by a straight series of carinal plates; spinelets 

 mostly one to a plate, small, rough, conical; intermarginal papular areas rather 

 large, subquadrate; adambulacrals monacanthid; numerous narrowly spatulate, 

 unguiculate, straight pedicellariae; tube-feot four-ranked; furrows wide. 



Description. — The carinal plates are easily distinguishable and are imbricated 

 directly, that is, without intermediate ossicles, into a fairly straight series, which 



