470 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



smaller, tubercle occurs at the junction of the first two brachials. The elements of the 

 IBr series and the first two lirachials are straight-edged and sharply flattened laterally, 

 with the margins of the dorsal surface flattened. 



The 10 arms were probably about 30 mm. long and are composed of smooth and 

 elongate obliquely quadrate segments. The length from the pro.ximal edge of the IBri 

 to the second syzj^gy is 5.5 mm. and the width of the first syzygy is 0.8 mm . The 

 distal intersyzygial interval is two to si.v, usually four, muscular articidations. The 

 arin^ taper more abruptly for the first 6 ram. of their length than they do distally. 

 The width at brachials 9 + 10 is already reduced to 0.6 mm. 



Pi consists of about 11 much elongated, cyhndrical, segments and is considerably 

 longer and stouter than the following pinnules, which decrease in length to about P, 

 and then gradually increase. Pa is present on all the arms. P2 has 9 segments, of 

 which the outer ones are slightly expanded and spinous at their distal ends; it is 2.4 

 mm. long. P3 with 8 segments is only 1.8 mm. long; its segments are more conspicu- 

 ously flared and spinous distally. The two basal segments of the later pinnules are 

 expanded and trapezoidal, but the following segments are slender. 



Locality .—Challenger station 192; near the Kei Islands (lat. 5°49'15" S., long. 

 132°14'15" E.); 256 meters; blue mud; September 26, 1874 [P. H. Carpenter, 1879, 

 1888; A. H. Clark, 1911, 1913] (1, B.M.). 



Remarks. — The only knowm specimen of this species, which served as the basis 

 of Carpenter's description in 1888, is evidently young with the mature characters 

 not yet fully developed. 



In revising the species of .iVntedonidae in 1907 I was unable to place this form with 

 any degree of certainty, and tentatively assigned it to the genus Nanometra. 



Later, however, I became impressed with its similarity to the young of Perometra 

 diomedeae and, suspecting that Carpenter might have overlooked the absence of P^, 

 I wrote to Prof. Bell, asking him to investigate the point for me. He replied: "I have, 

 as you requested, made an examination of the type of Carpenter's Antedon pmilla, 

 and so far as I can sec, there is no pinnule on the third brachial." In 1911 I pubhshed 

 a note on this species, definitely assigning it to the genus Perometra. After this note 

 was wTitten, but before it was published, I visited the British Museum and examined 

 the type specimen when I found, much to my surprise, that Pa was present on all the 

 arms. This information I inserted in a footnote. 



A study of the original specimen shows that this is a species of the genus Pero- 

 metra, but it differs from P. diomedeae in possessing Pa. [Note by A.M.C: However, 

 several specimens of diomedeae from off Kiu-.Shiu and from Sagami Bay, Japan, have 

 now been taken (see pp. 466-467) in which Pa is present.] The synarthrial tubercles 

 are also much more strongly developed than in P. diomedeae of equal size. The radials 

 have the characteristic features of the radials of P. diomedeae. 



PEROMETRA ROBUSTA (A. H. Clark) 



Figure 21 



Caryometra robuaia A. H. Clark, John Murray Exped. 1933-34, Sci. Reports, vol. 4, No. 4, 1937, 

 p. 95 (description; Mahahiss station 157), pi. 1, fig. 4. 



Diagnostic features. — The cirri are up to 20 mm. long when the arm length is 60 

 mm.; they arc rather stout basally, with 39-47 segments, the longer pro.ximal twice 

 as long as broad, the distal about twice as broad as long with a rounded dorsal spine; 



