644 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Bathymetrical range. From 79 to 242 (? 350) meters. 



Thermal range. From 3.20 to 8.30 C. ( 0.48 for the doubtful Bransfield 

 Strait specimen). [NOTE BY A.M.C.] No bottom temperature was obtained from 

 the Swedish South Polar Expedition station 5, to the east of Graham Land in the 

 Weddell Sea, but at the neighboring station 11 at 400 meters the temperature was 

 -1.10 O. 



Salinity range. From 33.79 to 34.15 parts per thousand. (34.34 for the Bransfield 

 Strait Specimen). 



History. This species was first mentioned under the name of Antedon hirsuta by 

 Dr. K. A. Andersson in 1904 and 1905 in a special study on the viviparity of some speci- 

 mens taken by the Swedish South Polar Expedition with the Antarctic on the Burdwood 

 Bank. 



In 19151 commented that Andersson's material belonged to a species closely related 

 to Isometra angustipinna if not identical with it. 



The detailed description and recognition of the species as new was carried out by 

 Dr. Th. Mortensen in 1917 and 1918. He recorded it from six Antarctic stations, two 

 of which were on the Burdwood Bank, two off Graham Land, and two much farther 

 north off southern Brazil. 



In 1920 Mortensen followed this by a very detailed account of the embryology and 

 development of the species. 



Gislen in 1924 included this species among those of which he studied the articula- 

 tions of the arms. 



The species was not found among the collections of the Terra Nova, German South 

 Polar Expedition, the Belgica, the Australasian Antarctic Expedition or the 

 B.A.N.Z.A.R.E. However, a number of specimens were taken by the Discovery In- 

 vestigations again on the Burdwood Bank as well as in the vicinity of the Falkland 

 Islands. Details of these were given by Dr. Dilwyn John in 1938. 



Some specimens were also obtained by the Scotia on the Burdwood Bank, but Vaney 

 in 1939 gave no details about them. 



ISOMETRA FLAVESCENS John' 



Isometra flavescens JOHN, Discovery Reports, vol. 18, 1938, p. 123 (listed), p. 124 (with Myzostomum), 

 p. 126 (range), p. 132 (in key), pp. 182-184 (station 160; description; comparisons), p. 187 (com- 

 parison with /. graminea), p. 192 (comparison with I. hordea); fig. 16, p. 182. 



Diagnostic features. The cirri are up to LX, 25-35; PI is much larger than P 2 

 (averaging 1.7 times the length of P 2 in eight specimens) with 9 to 14 segments; P 2 has 

 6 to 9 segments; P 3 (or P 4 ) is the first genital pinnule; the ventral surface of the disk, 

 except between the arm bases, is plated. 



Description (modified from John, 1938). The species is fairly small but robust. 

 The arms of all the twelve type specimens were broken but probably measured just over 

 40 mm. in length when complete. The length from IBr! to the second syzygy is from 

 8.5 to 10.5 mm. in ten specimens measured. 



The centrodorsal is conical and closely covered with cirrus sockets, which may, 

 however, leave free a small, bare, flattened dorsal pole. The sockets are arranged in 



*See also table 15 (p. 620), scatter diagram (p. 835), and Addenda (p. 837) under 1963. 



