A MONOGRAPH OF THE EXISTING CRENOIDS 261 



The pinnules in general resemble those of Pachylometra robusta; those in the 

 proximal portion of the arm are strongly carinate. 



The disk is covered with a pavement of very small plates. Side and covering plates 

 are well developed along the pinnule ambulacra. 



The color in alcohol is white. 



Notes. — The specimen from south of Timorlaut has 14 arms about 150 mm. long. 



In 1929 I described Perissometra occidentalis as follows: 



The centrodorsal is large, truncated conical, with the cirrus sockets arranged in 

 10 closely crowded columns of usually 3 each. 



The cirri are about XXV, 15-18, moderately stout, the longest from 30 to 35 mm, in 

 length. The first segment is very short, the second is longer, the third is about twice as 

 broad as long, the fourth is nearly as long as broad, and the fifth is about one-third 

 again as long as broad on the longest peripheral cirri, and very slightly longer than 

 broad on the other cirri. The following segments decrease in length so that the last 

 seven or eight before the penultimate are about as long as broad. The penultimate 

 segment is narrower than those preceding, and in lateral view is from one-third to one- 

 half again as long as broad. From the fifth onward the segments in lateral view have 

 slightly diverging ventral and dorsal edges, and their distal ends slightly overlap the 

 bases of the segments following. On the dorsal side the distal end of the segments may 

 be thickened so as to project considerably beyond the base of the succeeding segments, 

 giving the dorsal profile of the outer portion of the cirri a low and roundedly serrate 

 appearance. The opposing spine, which arises from the conspicuous white terminal 

 band on the penultimate segment, is transversely broadened, with the crest chisel-shaped 

 or strongly bilobate. 



The ends of the basal rays are visible as prominent rhombic tubercles in the 

 interradial angles. 



The radials are entirely concealed by the centrodorsal. The IBr! are very narrow 

 and bandlike, usually quite concealed by the centrodorsal except for a rounded median 

 tubercle and the very narrow and irregular lateral portions, which extend diagonally 

 outward, meeting those of the adjacent IBrj above the ends of the basal rays. The 

 borders of these lateral portions are sinuate, and the distal angle is usually produced 

 inwardly in the form of a conspicuous tooth which fits into a corresponding cavity be- 

 neath the lateral angle of the axillary. The IBr 2 (axillaries) are broadly rhombic with 

 the lateral angles slightly truncated forming short sides, which are about as long as the 

 length of the lateral portions of the IBr^ The median portion of the axillaries is 

 elevated, rising regularly into a very broadly rounded tubercle with the maximum 

 height in about the proximal third. The proximal border of the axillary, except in 

 the median line, is produced into a flangelike extension with a sinuous and more or less 

 irregular edge, the irregularities fitting into corresponding irregularities in the adjacent 

 border of the IBri. There are five IIBr series present, four of these being 4(3 + 4) and 

 one being 2. The division series are smooth dorsally and rise evenly to a very broadly 

 convex central portion. They are closely appressed against their neighbors. The 

 IIBr! are very short and their inner portion is extended distally and is terminated by a 

 short side at right angles to the lateral edge, which is usually more or less produced 

 inwardly in the form of a tooth fitting into a notch in the IIBr ? . 



