A MONOGRAPH OF THE EXISTING CRINOIDS 333 



The pinnules resemble those of the specimens described under imbricata, the 

 lower being strongly carinate. 



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

 covering plates are well developed along the brachial and pinnule ambulacra. 



The color in alcohol is white, the division series and arm bases as far as the third 

 brachial brownish. 



Hartlaub described the skeletal elements of the calyx from a preparation consisting 

 of the centrodorsal and radial pentagon made by Carpenter which he found in a special 

 vial with the Martinique specimens. This description by Hartlaub should be compared 

 with the description of the centrodorsal and radial articular faces of Crinometra brev- 

 ipinna var. insculpta given in Part 2, pp. 48, 49, figs. 76, 77, p. 53. 



Hartlaub says that the ventral surface of the centrodorsal is rather sharply pen- 

 tagonal, in good agreement with that of Perissometra inaequalis as figured by Carpenter. 

 The radial depressions are more or less sharply triangular, because the raised borders 

 of the basal grooves in part come into contact with each other at the entrance to the 

 central cavity of the centrodorsal. The circumference of the entrance to the central 

 cavity is sharply pentagonal. 



The dorsal surface of the radial pentagon shows a well developed basal star. The 

 inner ends of the rays are united with the rosette by ring-shaped bridges; the sharply 

 pointed outer ends reach to the border of the radial pentagon. The rays of the basal 

 star are three-edged ; inwardly they are in broad union with the rosette. With sufficient 

 treatment with caustic potash it is possible to isolate the basal rays with the rosette. 

 The isolated basal rays show on their inner end two perforations — the nerve canals. 

 All these features correspond in general to the same features in Perissometra angusticalyx 

 and in P. inaequalis. 



But considerable differences from P. angusticalyx and P. inaequalis are shown in 

 the ornamentation of the outer articular face of the radials. Especially striking, 

 according to Hartlaub, is the absence of a median ridge separating the two muscular 

 fossae. This is present in most endocylic comatulids, and also in Perissometra angusti- 

 calyx and P. inaequalis. Instead of this, there is, as in the Comasteridae, a median 

 groove that begins between the interarticular ligament fossae and farther out broadens 

 into an unpaired muscular fossa. This muscular fossa, in contrast to the conditions 

 in Perissometra angusticalyx and P. inaequalis, is not bordered by a sharp ridge but is 

 separated from the two small interarticular ligament fossae by a broad elevation which 

 in places is obscure. On the other hand, the dorsal ligament fossa lying below the 

 opening of the radial nerve canal is large and well developed, as in Perissometra inae- 

 qualis. The angle of inclination of the joint face is moderate and less strong than in 

 P. angxisticalyx, and in P. inaequalis. Finally, the dorsal surface of the radial pentagon 

 has approximately the same size as the ventral surface of the centrodorsal. In this 

 respect Hartlaub points out that there is agreement with P. inaequalis, while in the 

 specimen of P. angusticalyx figured by Carpenter the ventral surface of the centro- 

 dorsal is larger than the dorsal surface of the radial pentagon. Hartlaub said that in 

 general it should be noted that as yet it has not been determined to what degree of 

 variation the relation between the radial pentagon and the basal star is subject, and 

 therefore to what degree slight deviations in this region are of systematic significance. 



