660 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



The radials are almost or quite concealed by the centrodorsal. The IBr! are 

 short with slightly converging sides, almost concealed in the midline by the proximal 

 processes of the axillaries which are rhombic and as long as broad with the lateral angles 

 extending beyond the edges of the IBiv 



The ten arms were about 85 mm. long. The first brachial is deeply incised in the 

 median line by the proximal angle of the second. Inwardly the two first brachials 

 just meet beyond the distal apex of the axillary. The brachials between the first two 

 syzygies are oblong, about twice as broad as the median length, and the following ones 

 are very obliquely wedge-shaped, almost triangular, gradually becoming elongate 

 distally. The distal edges of the brachials are finely spinous. 



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

 of three muscular articulations. In one syntype from station 145 the first syzygy is 

 1.2 mm. in width. The other two specimens are of similar magnitude. 



PI is greatly elongated, with 30 or more segments; all are now (1958) broken. 

 The segments are relatively short, not more than twice as long as their proximal widths 

 and conspicuously flared and rugous at their distal ends, especially dorsally. P a is 

 similar, sometimes with rather stouter segments. P 2 and P b are considerably shorter 

 and stouter according to Carpenter. They are certainly stouter and with much 

 longer segments than P u still flared distally but not to the same extent. P 2 is the 

 first genital pinnule. In one specimen the gonads are swollen but in the others they 

 are more slender. The following pinnules appear to be similar to P 2 . 



Localities. Challenger station 145; off Marion Island Gat. 4643'00" S., long. 

 3804'30" E.); 255 meters; volcanic sand; December 27, 1873 (3, B.M.). 



Challenger; off Marion Island; 91-137 meters. 



Remarks.- Carpenter wrote (1888) that this species differs from the Atlantic 

 species of Hathrometra in the shortness of the later cirrus segments and in the characters 

 of the lower pinnules, of which the second pair is relatively large and stout with more 

 or less developed genital glands which do not appear in Hathrometra until the fourth 

 or even the fifth pair. These are especially large and well developed in the two ex- 

 amples from the lesser depth, and the segments of the pinnules which bear them are 

 proportionately stout. Another point of difference from Hathrometra is the greater 

 posterior projection of the axillaries, so that the IBr] are almost entirely concealed 

 in the middle line of the ray, while there is but little modification of the basal segments 

 of the distal pinnules. 



When I established the genus Thaumatometra in 1908, I assigned this species to 

 it because of the occurrence of a gonad on P 2 . But further study led me to believe 

 that this is not a feature of prime importance, and on the basis of Carpenter's description 

 and comments I adopted his view that this form is the southern representative of 

 Hathrometra tenella and FT. sarsi. 



The discovery early in 1924 of a closely allied species in the Gulf of Alaska and 

 the southeastern Bering Sea enabled me to determine that these two forms represent 

 a distinct genus showing affinites with such genera as Trichometra and Fariometra 

 and quite different from Hathrometra. 



Remarks [by A.M.C.]. I cannot agree with Mr. Clark that exigva is congeneric 

 with the North Pacific Retiometra alascana. Although the descriptions of the two are 

 not unlike and the numbers of cirrus and pinnule segments are similar, a comparison 

 of the actual type specimens has shown a number of differences in the shape of the 



