70 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



&'. The radial articular faces are never horseshoe shaped; there is always an abrupt change In 

 direction between the outer borders of the interartieular ligament fossie and the 

 proximal border of the dorsal ligament fossa. 

 c\ The muscular fosste are much smaller than the interartieular ligament fossae. 



d\ The muscular fossse, 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- 

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



to the rim about the central canal ZYGOMETRID^. 



e*. The Interartieular ligament fossse are roughly oblong, higher than broad, with their 

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



Zygometra coniata. 



e'. The interartieular ligament fossse are triangular, with their inner and outer borders 



making approximately the same angle with the transverse ridge. 



f. The inner side of the interartieular ligament fossre is convex and the outer side 



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



and the dor-sal ligament fossse are mutually united by their broadly truncated 



lateral angles Cntoptometra hartlauM. 



f. The inner and outer sides of the interartieular ligament fossre are straight ; the 



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



ligament fossse are entirely separated from their neighbors--^M(fiocn«us ornatus. 



d'. The muscular fossse are not boomerang shaped; in the rare eases in which they are 



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



the inner sides of the interartieular ligament fossie the vertical arm is much shorter 



than the horizontal. 



e'. The interartieular 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 fossse 



are very narrowly linear and scarcely evident Bimerometra martensi. 



e'. The interartieular ligament foss;e 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 fossse are conspicuous, broadly linear, or of various 



shapes. 



f^. The distal border of the interartieular ligament fossse is horizontal, convex with 



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



outer distal angles COMA.STERin.E. 



ff". The muscular and interartieular ligament fossse are nearly of the same size. 



Leptonemaster venustus. 

 g-. The muscular fossse are much smaller than the interartieular ligament foss-T. 

 ft\ The muscular fossse are triangular, with the inner apices of the triangles at 

 the sides of the intermuscular notch. 

 t\ The dorsal ligament fossa; are regularly semielliptical. 



Comatella nigra and C. stelHgcra. 

 i'. The dorsal ligament fossse have the proximal border strongly flattened. 



Capillaster multimdiata. 

 h'. The muscular fossaj are more or less band-liUe with approximately parallel 

 sides. 

 i\ The muscular fossre run rather strongly downward from their inner to their 



outer edges Coinatula Solaris. 



f. The muscular fosste are horizontal or convex with the chord of the convexity 

 horizontal. 

 f. The interartieular ligament fossse are as high as, or higher than, broad at 

 their narrowest part. 



