350 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL- 5° 



4. HELIOMETRA, gen. nov. 



Centro-dorsal hemispherical, bearing very numerous cirri without 

 definite arrangement, well distributed over the surface, but the pole 

 always free; cirri long, moderately stout, with numerous (30 to 80, 

 usually 40 to 60) segments, the proximal somewhat longer than wide, 

 the distal short, and provided with more or less prominent dorsal 

 spines; disk and ambulacra unplated; costals united by bifascial 

 articulation, rounded, never carinate, usually well separated; arms 

 always ten in number; brachials very numerous, always triangular 

 or more or less quadrate, more or less overlapping, never carinate 

 nor laterally compressed; syzygial joints between brachials 3 and 4, 

 9 and 10, and 14 and 15, or 16 and 17 (irregularly between 15 and 

 16) ; distally 2 to 6 bifascially articulated joints (most commonly 

 3 or 4) intervene between successive syzygia; proximal pinnules 

 greatly elongated and flagellate, the first and second always, and 

 usually the third and fourth, composed of very numerous joints 

 which are wider than long, at least in the basal half; the distal por- 

 tion of the lower pinnules is always more or less serrate or combed ; 

 distal pinnules slender and elongate, set closely together, the first two 

 joints expanded and trapezoidal, the others elongated. 



Color in life yellow, in one species more or less blotched with 

 white. 



Type of the genus. — Alecto eschrichtii J. Miiller, 1841. 



This genus corresponds to the "Eschrichti group" of Dr. Carpen- 

 ter, and contains at present eighteen described species. In addition 

 to these I have examined some undescribed forms from the neigh- 

 borhood of Shanghai. The distribution as at present known is : 

 Arctic and Antarctic seas, northern and southern Atlantic, entire 

 American coast of the Pacific, Bering Sea, Sea of Okhotsk, Sea of 

 Japan, and the coasts of the western Pacific, south at least to 

 Shanghai. 



The species of Heliomctra, taken as a whole, form a remarkably 

 homogeneous aggregation, the differential specific characters being, 

 when compared with those of the other genera of recent free crinoids, 

 very slight ; for instance, most of the well-known species of Hime- 

 rometra, to say nothing of the extraordinary Cyllometra manca, 

 exhibit more individual than Heliometra does generic variation. The 

 regular distribution of the syzygia is noteworthy, forming as it does 

 in several species a reliable specific character. No other genus has 

 the syzygia thus regularly placed, although an approach to it is 

 noticeable in Antedon. 



