A MONOGRAPH OF THE EXISTING CRINOIDS 269 



This form is less robust and rugged than the following (macrodiscus) with some- 

 what shorter and more slender cirri which are composed of fewer segments. 



Description. The centrodorsal is thick discoidal with the rather large bare polar 

 area flat or slightly concave. The cirrus sockets are arranged in two, or two and a 

 partial third, closely crowded irregular, or more or less regular, marginal rows. 



The cirri are XXXI-L, 30-35 (usually 30), 30 mm. long. All the segments are 

 subequal, about twice as broad as long, the basal somewhat shorter. The dorsal side 

 of the segments is perfectly smooth. The penultimate segment is comparatively 

 small, about as long as broad, with the dorsal surface convex. There may be a small 

 and weak opposing spine. The terminal claw is short and blunt, conical, and only 

 slightly curved. 



The radials are entirely concealed by the centrodorsal, or are very slightly visible. 

 The IBri are short and broad, oblong, about five times as broad as long, sharply 

 flattened and in close lateral apposition. The IBr 2 (axillaries) are triangular, about 

 twice as broad as long, and are also in close lateral apposition. A slight synarthrial 

 tubercle may or may not be present. 



The 10 arms are 190-200 mm. long, massive basally but tapering rather rapidly 

 and becoming comparatively slender after the basal third. They have a rough dorsal 

 surface. The first brachials are wedge-shaped, rather large, inwardly united for most 

 of their length, outwardly straight and in close apposition with those on the arms 

 adjacent. The second brachials are similar, but larger. They are wedge-shaped with 

 the shorter side inward, and are in contact with their neighbors outwardly, but not in- 

 wardly. The first syzygial pair (composed of brachials 3+4) is oblong, two and one- 

 half times as broad as long. The brachials following are very short, especially after 

 the thirteenth or fourteenth, and discoidal or broadly oblong. After the eleventh or 

 twelfth the brachials develop forward-projecting laterodorsal obtuse angles on the 

 distal edge on alternate sides of the median line which gradually become obsolete after 

 the basal third of the arm. The first nine or ten brachials have smooth distal edges. 

 Weak and low articular tubercles may be developed. There is a slight synarthrial 

 tubercle on the articulation between the first two brachials. The brachials beyond 

 the ninth or tenth have slightly overlapping distal ends. 



The first syzygy is between brachials 3+4 and the second usually between 

 brachials 9 + 10, though sometimes as early as brachials 7+8 or as late as brachials 

 14 + 15. The distal intersyzygial interval is from 3 to 16 (usually 9) muscular articu- 

 lations. 



PI is about 28 mm. long, and is composed of segments which for the most part 

 are about as long as broad. It is basally more or less webbed with perisome, and 

 tapers rapidly in its outer part. P 2 is slightly longer than Pj and stouter, especially 

 distally, the component segments being rather broader than long. The pinnules 

 following resemble P 2 but decrease gradually hi length to about the end of the proximal 

 fourth of the arm, where they are only 14 mm. long. All of these pinnules except P] 

 bear long fusiform gonads which reach nearly to their tips. In the second quarter of 

 the arm the gonad diminishes in length and more and more of the distal part of the 

 pinnule becomes slender; at the same time the pinnules gradually increase in length 

 reaching 24 mm. in the middle of the arm, where they are composed of about 60 

 elongated segments. After the proximal half of the arm the pinnules become entirely 



