522 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



In the type of Ps. inusitata the centrodorsal is small and conical, the sides hardly, 

 if at nil, convex, 3.2 mm. broad at the base and 2.4 mm. high. [Note by A.M.C: 

 If tlie figure given in the Siboga report is correct in the proportions of the centrodorsal, 

 the vertical height is also about 2.4 imii., so in this case, at least, Mr. Clark appears to 

 have made liis assessment of height in lateral view rather than along the surface of the 

 centrodorsal from apex to interradial edge.] The radial areas are delimited by very 

 narrow irregular bare spaces wliich at tbe periphery of the centrodorsal are rarely as 

 mucli as half as broad as tlie adjacent cirrus sockets, and are more or less encroached 

 upon by the sockets on either side so that their course is usually more or less zigzag or 

 irregular. They are scarcely to be recognized otherwise than that the outer columns in 

 each radial area are slightly separated from the outer columns in the adjacent areas 

 whereas within each radial area all the sockets are closely crowded together. Each 

 radial area contains 3 columns of cirrus sockets, the 2 outer of 4 each, the median of 2 

 only, being occluded apically by the outer columns coming together. At the dorsal 

 pole there are more or less numerous pits representing obsolete cirrus sockets. Some 

 of these are situated in the interradial lines, and their arrangement appears to be in 

 alternating rows instead of in columns. 



In the description of Ps. wireni Gislen gives the details of a young detached but 

 complete ciiTus. This was 10 mm. long with 18 segments, of which the first is short, 

 the second is about as long as broad, the third is three quarters again as long as broad, 

 the fourth is two and a half times as long as broad, and the fifth to seventh are from three 

 to three and a half times as long as broad; the following segments slowly decrease in 

 length so that the antepenultimate is two and a quarter times as long as broad and the 

 penultimate is twice as long as broad. The terminal claw is almost straight, half as 

 long as the penultimate segment. Gislen records also the occurrence of the first seven 

 segments of a fully grown cirrus. These are larger and stouter than the corresponding 

 segments in the j'oung cirrus, but of about the same proportions except for the third, 

 wliich is one third again as long as broad. This cirrus, according to Gislen, was 

 probably about 15 mm. in total length. 



In the type of Ps. immtata no basal rays are visible. The radials are even with 

 the run of the centrodorsal in the median line, but extend distalh' in the interradial angles 

 where their distal lateral angles are slightly separated. The IBr, are short, proximally 

 nearly 4 times as broad as long in the median line but with the sides converging so that 

 the distal border is only about 3 tunes the median length. They are widely separated 

 from their neighbors. The IBr2 (axillaries) are rhombic, half again as broad as long, 

 with the distal angle produced and the lateral angles extending far bevond the distal 

 lateral angles of the IBri. The synarthrial tubercle is only slightly indicated. 



In Ps. imreni the radials are only visible in the mterradial angles, and Gislen does 

 not mention the basal rays. Tlie IBr, are free laterally, 4 tunes as broad as long in the 

 median line, with converging sides. The IBrj are a third again as broad as long, 

 rhombic, with the lateral angles extending beyond the laterodistal angles of the IBrj, 

 the distal angle narrow and very much produced, and the proximal angle rounded. 

 There is a low synarthrial tubercle. 



In the tj-pe of Ps. immtata all the arms are broken. The first brachials are 3 

 times as long exteriorly as interiorl}^ and basally half again as broad as the exterior 

 length. The inner sides are entirely free, and make approximately a right angle with 

 each other. The outer sides just touch those of the first brachials on adjacent rays. 



