PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 661 



centrodorsal, size of the dorsal pole, form of the division series, and ornamentation of the 

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

 distal enlargement of the cirri 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 female genital pinnules is needed, I have little 

 doubt that exigua should be referred to Phrixometra. It differs from the other species 

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

 longer cirrus segments. 



PHRIXOMETRA NUTRIX (Morlensen) 



[See vol. 1, pt. 2, pi. 38, figs. 1232-1237] 



Thaumatomelra nutrix MORTENSEN, Wiss. Ergebn. schwed. Siidpolar-Exped. 1901-1903, vol. 6, 

 Lief. 8, 1918, pp. 15-18, pi. 5, figs. 1-7. A. H. CLARK, The Danish Ingolf-~Exped., vol. 4, No. 

 5, Crinoidea, 1923, p. 43 (locality), p. 56 (in key). GISLEN, Zool. Bidrag. 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). JOHN, 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). CUENOT in Grass6, Trait6 de Zool- 

 ogie, vol. 11, 1948, p. 55. DAWTDOFF in Grass6, Traite de Zoologie, vol. 11, 1948, p. 353 (larva). 



Phrixometra nutrix 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 comatulid 

 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, with less than 20 segments; P! 

 has about 14 segments; P 2 is usually the first genital pinnule and similar in length and 

 number of segments to Pj. 



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

 the base, with 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 IBr, are short with rounded lateral edges which are not 

 in contact with those of their neighbors. The IBr 2 (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. 



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

 2 muscular articulations. 



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. P 2 is exactly like P,, but 

 bears a gonad. P 3 and P 4 are a little shorter, with only 9 segments and without an 



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



