106 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Petasometra brevieirra H. L. Cl^bk, Mem. Mus. Comp. Zool., vol. 55, 1938, p. 36 (description; False 



Cape Bossut), figs. 1, 2, p. 37; Echinoderm fauna of Australia, 1946, p. 51. 

 Petasomelra variegata H. L. Clark, Mem. Mus. Comp. Zool., vol. 65, 1938, p. 38 (near Shell Islands, 



Darwin, 3-6 fathoms; description), figs. 3, 4, p. 39; Echinoderm fauna of Australia, 1946, 



p. 51. 



Diagnostic Jeatures.— There are 19-31 arms 80-85 mm. long. The cirri are XIX- 

 XXIII, 22-31, from 20 to 22 mm. long. 



Description. — The centrodorsal is thin-discoidal, with a broad flat dorsal pole 4 

 mm. in diameter. The cirrus sockets are arranged in a single regular closely crowded 



marginal row. 



The cirri are XIX, 28-31, from 20 mm. to 22 mm. in length. The cirrus segments 

 are subequal, about twice as broad as long, the basal shorter, the last 5 or 6 becoming 

 somewhat longer. The second segment has the distal dorsal edge produced and bluntly 

 serrate. On those following this serrate ridge in dorsal view becomes more and more 

 deeply crescentic, and on the fourteenth and following it becomes a median straight, 

 finely and rather bluntly serrate, transverse ridge which in lateral view appears as a 

 minute spine. The opposing spine is large, with the apex subterminal, arising from the 

 entire dorsal surface of the penultimate segment and equaling about one-half the 

 width of that segment in height. Owing to the closely crowded condition of the cirrus 

 sockets the first 3 segments of the cirri are sharply flattened laterally as in related 

 species. 



The radials are concealed by the centrodorsal in the midradial line, but are visible 

 as low triangles in the interradial angles of the calyx. The IBri are very short, about 

 6 times as broad as long, with the proximal and distal edges parallel to each other and 

 the lateral borders parallel to the middorsal line and not in contact with those of their 

 neighbors. The IBr^ (axillaries) are very broadly pentagonal, from 2 to 3 times as 

 broad as long, with the lateral borders, which are about two-thirds as long as those of 

 the IBri, diverging slightly. The anterolateral angles of the IBr, and the adjacent 

 proximal angles of the axUlaries are rounded off. There are in the type specimen 10 

 IIBr series of 4 (3 + 4), and 2 IIIBr series of 4 (3 + 4) both of which are developed on 

 the same IIBr series. The division series are strongly rounded dorsally, and resemble 

 those of Heterometra savignii; their component elements do not have extended ventro- 

 lateral borders. 



The 22 arms of the type specimen are 85 mm. in length. The first 2 brachials are 

 subequal, slightly wedge-shaped, about 4 times as broad as the median length. The 

 first are interiorly united for the proximal two-thirds, beyond the point of imion 

 diverging at a right angle. The fu-st syzygial pair (composed of brachials 3+4) is 

 oblong, two and one-half times as broad as long. The next 4 brachials are short, 

 approximately oblong, about 4 times as broad as long, those following becoming 

 obUquely wedge-shaped, two and one-half times as broad as long, and less obliquely 

 wedge-shaped distally. 



Pa is always absent. Pd is from 11 mm. to 12 mm. in length and is composed of 

 27-29 segments of which the first 4 or 5 are broader than long and the remainder are 

 about as long as broad, becoming slightly longer than broad terminally. The pinnule 

 is moderate in size, smooth, evenly tapering, and very delicate distally. Pj is 10 mm. 

 long with 22 segments, resembling Pd but very slightly more slender. Pj is 10 mm. 

 long with 25 segments, resembling P,. P3 is 6 mm. long with 19 segments, smaller and 



