A MONOGRAPH OF THE EXISTING CRINOIDS 35 



Hartlaub said that after the removal of the cirri the centrodorsal shows five strong 

 interradial ridges and five weaker midradial ridges. As a result of the presence of 

 these ten ridges the ventral surface of the centrodorsal is rather decagonal than pen- 

 tagonal. The radial grooves are approximately triangular, the basal grooves moder- 

 ately deep and broadened in the middle. The opening of the central cavity shows ten 

 convex projections. 



The dorsal surface of the radial pentagon is approximately pentagonal, with a 

 well-developed basal star. The rosette and basal bridge are well developed. The 

 basals almost always show in the middle of the ventral surface a sharp carination. 

 The dorsal surface of the basal rays shows irregular unevennesses. The peripheral 

 ends are sometimes reduced, sometimes broad, in basal rays from the same specimen, 

 these structures appearing to be rather variable even in a single example. Centrally 

 the basal rays are set off from the rosette part by a weak, necklike connection. The 

 rosette part shows on the ventral surface two small openings, on the dorsal surface a 

 single large opening. 



The sculpture of the articular faces of the radials, according to Hartlaub, is well 

 marked and, though minor variations occur, the main features are constant in different 

 individuals (see Part 2, p. 46, figs. 72, 73, p. 43). A median vertical ridge is present, 

 through this is short since the distal border has a broad and deep median incision. 

 It is only slightly raised, very broad, and very deep since the excavations of the joint 

 surface abut against it hi the form of niches. The muscular fossae arc in general 

 rather flat and are separated from the somewhat more deeply excavated interarticular 

 ligament fossae by prominent diagonal ridges. The relatively strong development of 

 the dorsal ligament fossa is striking. The central canal is situated approximate!}- in 

 the center of the articular face. At the base of the radials are two lateral knobs directed 

 dorsally, forming with the corresponding structures of the neighboring radials bases 

 against which the interradial ridges of the centrodorsal rest. The central cavity, as 

 viewed ventrally, is bordered by five vertical pairs of laminae, the floors of the mus- 

 cular fossae, the five pairs being separated by five radial notches. The components 

 of these pairs are separated by deep interradial clefts. Since the upper ends of the 

 laminae are curved the circumference of the central cavity has a scalloped appearance. 



Carpenter's original description, based upon the specimen in the Paris Museum 

 collected by Duchaissaing in 1870, was as follows: 



Cirri 12-20; long and slender, composed of 40-60 joints, the later ones of which bear dorsal spines. 

 The rays may fork four times, each subdivision consisting of 2 joints not united by a syzygy. Usually, 

 however, there are not more than 2 axillaries, the distichal [IIBr] and the palmar [IIIBr], above the 

 radials [radials and IBr series]; and palmars are frequently only developed upon the inner pair of the 4 

 secondary arms; so that there are 30 arms in all (as in the Paris specimen), viz., 6 on each ray, in the 

 following order: 1, 2, 2, 1. Tolerably large, sharp spines are scattered irregularly over the calyx and 

 arm bases. The ami-joints are triangular in outline, alternating with one another from side to side; 

 and from near the base of each triangular surface there rises a strong curved spine, which projects 

 forwards and slightly outwards. On the lower parts of the arms, therefore, there is a double row of 

 these spines alternating right and left of the median dorsal line; but farther out, as the joints become 

 more and more compressed laterally, the two rows gradually coalesce into a single median one, the 

 spines at the same time becoming less and less prominent. The disk bears a fairly complete anam- 

 bulacral plating, and there is a double row of plates along each edge of the pinnule ambulacra, viz., 

 side plates resting on the pinnule joints and supporting the covering plates which overlap one another 

 alternately from opposite sides. The color varies from almost white through pale straw color to a 



