PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 715 



centrodorsal, the cirrus sockets being in closely crowded alternating rows, wliercas in 

 Poliometra they are in definite columns, and by the distal intersyzygial interval which 

 is 3 muscular articulations and not 4 as in Poliometra. 



From small individuals of Ileliometra glacialis it is distinguished by the more or 

 less sharplj' conical instead of flattened hemispherical centrodoreal, by the color, which 

 in Heliometra is bright j-ellow, by the distal intersyzygial interval, which is 3 muscular 

 articulations instead of 4 as in Ileliometra, and by the character of P,, which is exceed- 

 ingly slender, but stiff'ened, with all the segments except the basal greatly elongated 

 with prominent spines on their distal ends. 



The absence of the prominent spinous eversion of the distal ends of the earlier 

 brachials easily distinguishes this form from any of the species of Trichometra. 



Description. — The centrodorsal resembles that of //. tenella, but is usually some- 

 what lower, and the cirrus sockets are not so numerous. 



The cirri are XL-LXX, 14-24 (most frequently 17-21) from 11 to 17 mm. (usually 

 between 13 and 15 mm.) in length, resembling those of H. tenella but more slender 

 with the earlier segments usually more elongate. 



The radials, post-radial series and arms resemble those of H. tenella. The arms 

 are from 35 to 90 mm. (usually between 40 and 65 mm., and rarely over 70 mm.) in 

 length. 



Syzygies occur between brachials 3+4, 9 + 10, 14 + 15, and distally at intervals of 

 3 muscular articulations, very exceptionally 4. In a tabulation of 85 cases the inter- 

 syzygial interval was found to be 3 muscular articulations in 76, 4 in 5, and 2 in 4. 



Pi is from 10 to 10 mm. (usuallj' about 13 mm.) in length, with 25 to 42 (usually 

 between 30 and 35) segments. The first three segments are about as long as broad, 

 the fourth is about half again as long as broad, and the following rapidly become 

 elongated and exceedingly slender and from three to four times as long as broad distallj^; 

 the fourth and following segments have somewhat flaring and overlapping distal ends 

 set with fine spines. P2 is from 3 to 5 mm. (usually between 4 and 5 mm.) long with 

 8 to 12 (usually 9 or 10) segments, basaUy slightly stouter than P, and tapering rapidly 

 to a very delicate tip; the fii-st segment is not quite so long as broad, the second is 

 about as long as broad, the third is rather longer than broad, the fourth is about twice 

 as long as broad, and the remainder gradually become elongated and slender, and 

 excessively long and slender distally. 



P3 is from 3 to 5 mm. (averaging 3.8 mm.) long with 8 to 13 (usually 12) segments, 

 resembling Pj. 



In the distal pinnules the first segment is short and trapezoidal with the outer 

 (longest) edge concave, the second is about twice as long as the first and trapezoidal, 

 the third is about two and a half times as long as broad, and the fourth and follow- 

 ing are about three times as long as broad, becoming somewhat longer distally. On 

 the third and following segments the distal ends are everted and armed with fine 

 spines. 



Grieg (1913) says that in life this species is light grayish brown with narrow darker 

 bands; Alder (1800) describes it as light grajish brown. 



Localities. — Fish Hawk station 1124; off Martha's Vineyard Gat. 40°01' N., long. 

 68°54' W.); 1170 meters; temperature 3.89° C; fine sand, green mud, and calcareous 

 nodules [Verrill, 1884] (2, U.S.N.M., 24105, 35876). 



