654 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Genus PHRIXOMETRA A. H. Clark 



Antedon (part) P. H. CARPENTER, Challenger Reports, Zoology, vol. 26, pt. 60, 1888, pp. 185, 186, pi. 

 30, figs. 1-3. 



Thaumatometra (part) MOHTENSEN, Wiss. Ergebn. schwed. Siidpolar-Exped. 1901-1903, vol. 6, Lief. 8, 

 1918, p. 15; Studies in the development of cnnoids, 1920, pp. 56-58 (development), fig. 8, pi. 28. 

 A. H. CLARK, The Danish /rego/f-Exped., vol. 4, No. 5, Crinoidea, 1923, p. 43 (locality), p. 56 (in 

 key). 



Phrixometra A. H. CLARK, Journ. Washington Acad. Sci., vol. 7, 1917, No. 5, p. 128 (referred to the 

 Bathymetrinae), p. 131 (diagnosis; type species Antedon longipinna P. H. Carpenter, 1888; 

 range; included species); No. 16, p. 511 (in key; range); Unstalked crinoids of the Siboja-Exped., 

 1918, p. 246 (in key; range), p. 253. JOHN, Proc. Linn. Soc. London, sess. 149, pt. 2, 1937, p. 86; 

 Discovery Reports, vol. 18, 1938, p. 125 (genus previously known only from off the river Plate), 

 pp. 164-174 (includes P. longipinna with the new variety antarctica, nutrix (Mortensen) and 

 raynerisp. nov.). GISLN, Rep. Swedish Deep Sea Exped., vol. 2, Zool., No. 4, 1951, p. 55 (depth 

 range). HYMAN, The invertebrates, vol. 4, Echinodermata, 1955, p. 75. 



Diagnosis. A genus of the Bathymetrinae with the cirri XXX-L, 12-25, the 

 peripheral cirri with the longest segments two to about three times as long as their 

 median width and the distal ones about as broad as long, rarely longer; the brachials 

 are more or less spinous at their distal ends; the oral pinnules have up to 30 segments, 

 which, after the first one or two, are longer than broad and the outer ones are markedly 

 flared and spinous at their distal ends; the genital pinnules of the female each have a 

 pouchlike marsupium alongside the ovary. 



Type species. Antedon longipinna P. H. Carpenter, 1888. 



Geographical range. Known from off Uruguay to the Burdwood Bank, Clarence 

 Island and the Bransfield Strait area, the Shag Rocks, South Georgia, and off Marion 

 Island. 



Bathymetrical range. From 137 (?91) to 1097 meters. 



Thermal range. From 0.48 to +3.20 C. 



Salinity range. From 34.22 to 34.34 parts per thousand. 



Remarks [by A.M.C.]. The presence of a marsupium made of skin on each genital 

 pinnule of the female of Antedon longipinna and Thaumatometra nutrix is enough to 

 distinguish them generically from the other species of the subfamily. The question is 

 whether each should be isolated in a distinct genus on the grounds of the similarity of 

 the oral and genital pinnules in nutrix as opposed to their marked difference in size in 

 longipinna. Only a single small specimen of the third species P. rayneri is known. It 

 has P 2 longer than P! and P 3 , the latter being the first genital pinnule. Dr. Dilwyn John 

 was convinced of a close relationship between the three species, so I am accordingly 

 leaving them together. At the same time I am including in this genus Antedon exigua 

 P. H. Carpenter as explained on p. 652. Female specimens are not known but except 

 for larger numbers of pinnule segments and longer cirrus segments the characters agree 

 well with those of the species of Phrixometra. 



KEY TO THE SPECIES AND SUBSPECIES OF PHRIXOMETRA 



[by A.M.C.] 



a'. Cirri with 20-25 segments (off the coast of Uruguay; 1097 meters). 



longipinna longipinna (p. 655) 

 a 2 . Cirri with up to 20 segments. 

 6 1 . Cirri about XLV or more. 



c 1 . The first genital pinnule shorter and with fewer segments than the preceding oral pinnule. 



