MONOGRAPH OF THE EXISTING CRINOIDS. 11 



transverse (greater) diameter of the central canal. It is slightly constricted 

 between the muscular fossae. 



The cavity on the ventral surface of the radial pentagon is filled nearly to 

 the height of the distal edges of the muscular fossae with a loose calcareous 

 deposit showing no central canal. 



Diameter of radial pentagon at base, 3 mm. ; height of articular face, 1.3 mm. ; 

 width, at transverse ridge, 2 mm.; distance from center of rosette to middle of 

 dorsal outer edge of radial, 1.3 mm. ; distance from center of ventral face of radial 

 pentagon to middle of ventral edge of radial, 0.8 mm.; to apex of interradial 

 angle, 1.5 mm. 



COMATILIA IRIDOMETRIFORMIS. 

 Figs. 13, 14, p. 15. 



The articular faces of the radials are entirely and widely separated from 

 each other, just as in Neometra, by broad interradial processes formed by the 

 produced lateral edges of two adjacent radials. The outline of each radial face 

 as a whole is approximately semicircular. The production of the lateral edges 

 of the radials has produced a corresponding distortion of the elements of the 

 articular faces, these being laterally curved outward and somewhat elongated 

 transversely. 



The dorsal ligament fossa is deep, and about two and one-half times as broad 

 as high. The ligament pit is very narrow, though nearly as wide as the trans- 

 versely oval central canal. 



The interarticular ligament fossae are triangular, with their inner apices 

 on the level of the distal border of the central canal. The proximal and distal 

 edges make approximately the same angle with the horizontal, and are nearly 

 straight; the outer edges, which are about two-thirds the length of the other 

 two, are somewhat convex. 



The muscular fossae form elongated triangles with their apices outward. Their 

 greatest height is equal to the distance from their lower borders to the transverse 

 ridge; their inner edges are strongly convex. 



A broad undifferentiated area incloses the central canal and extends laterally 

 in the form of a long angle to the ends of the transverse ridge, its distal border 

 following, and being delimited by, the proximal border of the interarticular liga- 

 ment fossae; anteriorly (distally) this area is continued as a narrow intermus- 

 cular septum concave on the summit which rapidly diminishes in height, being 

 replaced after the proximal third of the muscular fossae by a narrow intermus- 

 cular furrow. 



The ventral surface of the radial pentagon, which is sharply stellate, is 

 covered by a somewhat concave loose calcareous deposit showing a small central 

 canal. The produced interradial angles, and a border equal to one-half of the 

 width of these interradial processes about the distal edges of the radial faces, 

 are free from any secondary calcareous covering. 



