70 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



b 3 . The radial articular faces are never horseshoe shaped; there is always an abrupt change in 

 direction between the outer borders of the liiterarticular ligament fossae and the 

 proximal border of the dorsal ligament fossa. 



c'. The muscular fossae are much smaller tb:m the interarticulnr ligament fossae. 

 d\ The muscular fossa?, which are boomerang shaped with the two arms of the boomerang 

 approximately of the same length, curve about the inner distal angle of the inter- 

 articular ligament fossa; and pass downward along their inner edges nearly or quite 



to the rim about the central canal ZYGOMETRID.E. 



&. The interarticular ligament fossae are roughly oblong, higher than broad, with their 

 inner and outer edges more or less perpendicular to the transverse ridge. 



Zygometra comata. 

 e*. The interarticular ligament fossa? are triangular, with their inner and outer borders 



making approximately the same angle with the transverse ridge. 

 f. The inner side of the interarticular ligament fossa? is convex and the outer side 

 is concave; the proximal border of the dorsal ligament fossa is evenly convex 

 and the dorsal ligament fossa? are mutually united by their broadly truncated 



lateral angles Catoptometra hartlauU. 



f. The inner and outer sides of the interarticular ligament fossa? are straight; the 



proximal border of the dorsal ligament fossa is strongly flattened; the dorsal 



ligament fossa? are entirely separated from their neighbors__B(itocrius ornatus. 



d'. The muscular fossae are not boomerang shaped; in the rare cases in which they are 



transversely elongate and extend around the inner distal angle and downward along 



the inner sides of the interarticular ligament fossae the vertical arm is much shorter 



than the horizontal. 



e 1 . The interarticular ligament fossa? are large and rectangular, with their inner and 

 outer sides parallel and (except just at the base) perpendicular to the transverse 

 ridge and their distal sides parallel to the transverse ridge; the muscular fossae 



are very narrowly linear and scarcely evident Hiinerometra martensi. 



<?. The interarticular ligament fossa? are not rectangular, but their distal or inner 

 borders, or both, are more or less convex, and their outer borders are more or less 

 convergent; the muscular fossa? are conspicuous, broadly linear, or of various 

 shapes. 



f 1 . The distal border of the interarticular ligament fossa? is horizontal, convex with 

 the chord of the convexity horizontal, or slopes downward from the inner to the 



outer distal angles COMASTERID^E. 



g 1 . The muscular and interarticular ligament fossa? are nearly of the same size. 



Leptonemaster venustus. 



g-. The muscular fossa' are much smaller tl'ian the interarticular ligament fossa?. 

 ft 1 . The muscular fossae are triangular, with the inner apices of the triangles at 



the sides of the intermuscular notch. 

 i 1 . The dorsal ligament fossa? are regularly semielliptical. 



ComateHa nigra, and C. steJligera. 

 f. The dorsal ligament fossa? have the proximal border strongly flattened. 



Gapillaster multiradintn. 

 h'. The muscular fossa? are more or less band-like with approximately parallel 



sides. 

 i 1 . The muscular fossa? run rather strongly downward from their inner to their 



outer edges Comatula Solaris. 



i'. The muscular fossa? are horizontal or convex with the chord of the convexity 



horizontal. 



/'. The interarticular ligament fossae are as high as, or higher than, broad at 

 their narrowest part. 



