MONOGRAPH OF THE EXISTING CRINOIDS. 49 



angle of the interarticular ligament fossae. The muscular fossae are separated 

 interiorly by a shallow furrow, which expands somewhat at the proximal end, the 

 sides of which are parallel and about as far apart as one-half the horizontal 

 diameter of the central canal. The muscular fossse bear three strongly marked 

 equidistant narrow ridges parallel to the distal border. 



The ventral surface of the radial pentagon is obscured by a small plug of 

 spongy calcareous deposit, which is almost completely separated from the radials 

 themselves by five large circular radial gaps and numerous smaller ones. 



The furrow between the radials extends to the height of the most distal 

 of the three ridges on the face of the muscular fossae. 



Diameter of radial pentagon at base, 5.6 mm. ; height of articular face (meas- 

 ured along the inclination), 2.9 mm.; width, at transverse ridge, 2.2 mm.; dis- 

 tance from center of rosette to middle of dorsal outer edge of radial, 2.3 mm.; 

 diameter of ventral intermuscular space, 1.2 mm. 



PACHYLOMETRA IN.EQUALIS. 



See figs. 086, 9S7, pi. 3. 



PERISSOMETRA ANGUSTICAI/TX. 



See figs. !)84, 985, pi. 3. 



PO2CILOMETRA ACCELA. 

 See figs. 988, 989, pi. 3. 



CHAR1TOMETRA BASICURVA. 

 See figs. 990, 991, pi. 3. 



CHARITOMETRA INCISA. 

 See figs. 902, 993. pi. 3. 



MACROPHREATA. 



The radial articular faces of the Macrophreata exhibit a remarkable homo- 

 geneity, in sharp contrast to the plasticity apparent in the same structures in the 

 oligophreate families; in fact, the entire range of variation found in the Macro- 

 phreata is less than that seen in any of the larger oligophreate families, excepting 

 only the Zygometridse. 



Thus an examination of the radial articular faces, no less than a close exami- 

 nation of the other structures, emphasizes the homogeneity of this group as now 

 understood. 



The radial pentagon of the macrophreate forms differs from that of the 

 oligophreate species in three essential particulars: (1) There is no calcareous 

 deposit on the inner surface of the radials nor upon the ventral surface of the 

 rosette, so that there is no trace of any central plug; (2) the plane of the mus- 

 cular fossae is nearly or quite parallel to the dorsoventral axis of the animal, so 



