ASTEROIDEA 159 



plates of irregular outline, measuring o-o6-o-i8 mm. in diameter, with as many as three 

 layers of trabeculae in the centre. There are no integumentary spinelets or prickles such 

 as characterize P. mira (de Loriol). 



In comparison with P. inflata Fisher this particular specimen has a more flaccid 

 body wall with obviously weaker skeleton, much fewer actinal intermediate spines, 2 

 inferomarginal spines (instead of i) over most of ray; while the strong grooving of the 

 actinal, adambulacral and oral spines of inflata is only faintly suggested in the furrow 

 spines of echinaster. Our specimen of echinaster has i intermarginal spine at base of 6 

 out of 10 intermarginal areas. There are only a few inconspicuous intermarginal spine- 

 lets on the type of inflata but another specimen from the same region (Monterey Bay, 

 California) has 8 13 in i or 2 intermarginal series. 



P. inflata has been dredged from off Oregon to San Diego, CaUfornia, 26-159 fathoms 

 (Fisher, 191 1, p. 264). P. inflata flexilis is apparently a deeper water race (334-600 

 fathoms) from California and probably extends to the Gulf of Panama, 458 fathoms 

 (Ludwig, 1905, p. 210, as Alexandraster yniriis). P. flexilis has a very delicate skeleton 

 (Fisher, 1911, p. 265, pi. 64; pi. 112, fig. 2), slender acicular spines and no deposits in 

 the abactinal integument. 



H. L. Clark has described P. capensis from 160 and 230 fathoms. Cape Colony. It 

 closely resembles our specimen of P. echinaster which is derived from a station (Gough 

 Island) that is nearer to South Africa than to Tierra del Fuego. 



Clark (1923, p. 291) has raised the question whether his species is specifically distinct 

 from echinaster. The presence of 2 inferomarginal spines on many of the plates of his 

 second specimen (1926, p. 20) is a character of echinaster shared by the Gough Island 

 specimen. His larger specimen (R 68 mm.), with 2 inferomarginal spines, has the spines 

 in general markedly sacculate which is not the case in echinaster, nor in inflata. Ob- 

 viously a definitive decision must be postponed until an adequate series of specimens is 

 available. 



It is curious that a locality so near to Cape Horn as the Gulf of San Mathias, Argentina, 

 would yield such a distinctly diff'erent species as P. mira (de Loriol), 1904. In this form 

 the abactinal spines have a flattened, often capitate, tip, and are quite short and tuber- 

 cular. In addition to the spines, the surface of the body is covered by a mukitude of 

 almost microscopic thorny spinelets (de Loriol, 1904, p. 33, pi. 3, fig. 1-1 h). 



The only other species which has dermal spinelets is P. japonica Fisher from 182 

 fathoms oflF Honshu, Japan. This differs from P. inflata, the geographically nearest 

 form, in having a decidedly broader abactinal area with more numerous abactinal spines, 

 numerous delicate thorny spinelets immersed in the thick membrane of the papular 

 areas, more widely spaced inferomarginal spines (often 2 to a plate as in echinaster) and 

 adambulacral spines without a well-marked groove. The dermal spinelets are smaller, 

 slenderer, and less numerous than those of P. mira. 



Type locality. Nassau Bay, Tierra del Fuego, 95 m. 



