A MONOGRAPH OF THE EXISTING CRINOIDS 83 



PARAMETRA LISA. ap. DOT. 



Diagnostic features. -The arms beyond the proximal more or less oblong brachials 

 are distinctly carinate; and the cirri, which are arranged in 10 columns on the centro- 

 dorsal and are about one-quarter of the arm length with 25-26 segments, have the 

 transition segment the eighth, and the distal segments as long as broad with very small 

 and obscure dorsal processes. The 19 arms are 115 mm. long, and the cirri are 20-28 

 mm. long. 



Description. The centrodorsal is low, conical, with a low rounded conical dorsal 

 pole. The cirrus sockets are arranged in 10 columns of usually two each, there being 

 two columns in each radial area. The columns are in close contact interradially, but 

 are slightly separated in the mid-radial lines. 



The cirri are XXI, 25-26, from 20 to 28 mm. in length, and rather slender. The 

 first segment is very short, the second is about twice as broad as long, the third is 

 slightly broader than long, the fourth is about one-third again as long as broad, and 

 those following gradually increase in length to the eighth, a transition segment, which 

 is between two and one-half and three times as long as its least width. The segments 

 following gradually decrease in length so that the last 15 or 16 are about as long as 

 broad. The basal portion of the cirri tapers slightly and slowly to the transition 

 segment. The sides of the transition segment converge very slightly to the beginning 

 of the distal third, then diverge to the end. Beyond the transition segment the cirri 

 remain of the same width to the tip. On the transition and following segments the 

 median portion of the distal border dorsally is roughened or armed with exceedingly 

 fine spines. On the succeeding segments it becomes slightly produced and also nar- 

 rowed, the profile of the outer portion of the cirri being slightly serrate dorsally. The 

 processes almost disappear on the antepenultimate segment. The penultimate seg- 

 ment is usually a truncated cone, with no trace of an opposing spine. The terminal 

 claw is about as long as the penultimate segment; it tapers gradually to a sharp point 

 and is only very moderately curved. The penultimate segment and the terminal 

 claw appear practically as a single unit. Often, however, there is a slight median or 

 subterminal tubercle representing the opposing spine on the penultimate segment, in 

 which case the terminal claw is usually shorter and more strongly curved. The long 

 peripheral cirri, none of which are fully developed, lack the transition segment, and 

 practically all traces of dorsal processes. 



The radials are almost entirely, or even quite, concealed by the centrodorsal. 

 The IBr t are very short, longer laterally than in the median line, and in contact later- 

 ally. The IBr 2 (axillaries) are in the median line three times as long as the IBri or 

 even longer. They are rhombic with truncated lateral angles, and are about half 

 again as broad as long. Their lateral edges converge slightly proximally and are not 

 in contact with those of their neighbors. In the proximal third they bear a fine median 

 elevated line which continues a similar median line on the IBi'i. The IIBr series and 

 IIIBr scries (when present) resemble the IBr series. The inner borders of the IIBri 

 and of the first brachials may be slightly everted. 



The 19 arms are 115 mm. long. Five IIBr series are present, one on each post- 

 radial series. Four of the IIBr scries bear externally a IIIBr series. All the division 

 series are 2. A very narrow, low, inconspicuous, but always distinct, carinate line 

 runs along the middorsal line of the arms to their tips. 



