PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 661 



centrodorsal, size of the doi-sal pole, form of the division series, and ornamentation of the 

 pinnule segments. Though the proportions of the cirrus segments may he similar, the 

 distal enlargement of the eirri in exigua is not shared by alascana, whereas it does 

 occur in some specimens of Phrixometra, notably of P. longipinna antarctica. Although 

 confirmation from examination of the fenude genital pinnules is needed, I have little 

 doubt that exigua should be referred to Phriiometra. It diflfers from the otlier species 

 of the genus mainly in the shorter, more numerous segments of P, and the relatively 

 longer cirrus segments. 



PHBIXOMETRA NUTRIX (Mortensen)' 



[See vol. 1, pt. 2, pi. 38, figs. 1232-12.37] 



Thaumalometra nulrix Mortensen, Wiss. Ergebn. schwed. Siidpolar-Exped. 1001-1903, vol. 6, 

 Lief. 8, 1918, pp. 15-18, pi. 5, figs. 1-7. — A. H. Clark, The Danish /n^o^Z-Exped., vol. 4, No. 

 5, Crinoide.i, 1923, p. 43 (locality), p. 56 (in key). — Gisl^n, Zool. Ridrag. Uppsala, vol. 9, 1924, 

 p. 28 footnote 1, p. 195 — A. H. Clark, Sci. Rep. Australasian Antarctic Exped., 1911-14, ser. 

 C, vol. 8, pt. 4, 1937, p. 5 (listed), p. 6 (doubtful member of genus), p. 8 (in key). — Jojin, Proc. 

 Linn. Soc. London, sess. 149, pt. 2, 1937, p. 86 (Antarctic and from Burdwood Bank), p. 87 

 (protection of brood), p. 88 (brood pouches and larvae). — Cu£not in Grassfi, Trait<5 de Zool- 

 ogie, vol. 11, 1948, p. 55. — Dawydoff in Grass6, Traiti? de Zoologie, vol. 11, 1948, p. 353 (larva). 

 Phrixometra nulrix John, Discovery Reports, vol. 18, 1938, p. 123 (listed), p. 125 (viviparous), p. 126 

 (in table), p. 128 (brood pouches on adoral or aboral side of pinnules; young emerge in comatuhd 

 form; pentacrinoids within pouch), p. 129 (distribution table), p. 132 (in key), pp. 170-172 

 (station; description of new material); fig. 11, p. 171. — Hyman, The invertebrates, vol. 4, Echi- 

 nodermata, 1955, fig. 28E (pinnule with pentacrinoids), p. 75 (free swimming larval stage 

 suppressed) . 



Diagnostic features. — The cirri are about XLV, wnth less than 20 segments; Pj 

 has about 14 segments; P2 is usually the first genital pinnule and similar in length and 

 number of segments to P,. 



Description. — The centrodorsal is rounded conical, about half as high as broad at 

 the base, \vith the dorsal pole convex and a little roughened and the cirrus sockets 

 closely crowded. The rim is regular, and not produced interradially. 



The cirri are about XLV. Only a few of the peripheral ones which are not yet 

 fully developed remain; judging from these the number of segments is about 20. No 

 dorsal spines are developed on these young cirri, but, judging from the cirri of the pen- 

 tacrinoids, there must be at least an opposing spine on the fully developed cirri. The 

 proximal segments of the cirri are longer than broad, the distal much shorter; but it 

 is uncertain whether this is also true of fully developed cirri. 



The radials are very short in the median line, but their interradial angles are 



somewhat produced. The IBri are short with rounded lateral edges wiiich are not 



in contact with those of their neighbors. The IBr2 (axillaries) are as broad as long. 



The arms are 10 in number; the brachials have a row of short spines along the 



raised distal edge. 



Syzjrgies occur between bracliials 3+4, 9 + 10, and 14 + 15, thence at intervals of 

 2 muscular articidations. 



P, is from 3 to 4 mm. long, composed of 14 slender and somewhat elongated seg- 

 ments, the distal edges of which are fringed with spines. Pj is e.xactly Uke P,, but 

 bears a gonad. P3 and P4 are a little shorter, with only 9 segments and without an 



* See also Addenda (pp. 836, 837) under 1962 and 1963. 



