MONOGRAPH OF THE EXISTING CRINOIDS. 



75 



ft'. The distal border of the muscular fossie is convex with the chord of the con- 

 vexity parallel to the transverse ridge, or rises from the inner to the outer 

 distal angles. 

 i\ The outer borders of the muscular fossae are straight; the centrodorsal bears 

 a single row of cirrus sockets. 

 /'. The muscular fossie are separated interiorly by a narrow intermuscular 



ridge Cyllometra alhopurpurea. 



f. The muscular foss:e are separated interiorly by a broad intermuscular 



groove Cyllometra disciformis. 



i'. The outer borders of the muscular fossae are more or less concave; the centro- 

 dorsal bears regular columns of cirrus sockets, at least two to a column. 

 p. The muscular fossfe have the inner distal angle very broadly, and the 

 outer distal angle very narrowly, rounded, and the outer borders rather 

 strongly concave; the centrodorsal bears the cirrus sockets in 15 



crowded columns Thalassometra villosa. 



f. The muscular fossie have the distal border evenly convex. 



k\ The interior length of the muscular fossse is three times their width ; 

 the cirrus sockets are in 10 well spaced columns. 



Stiremetra ^reviradia. 



k'. The interior length of the muscular fossse is much less than three times 



their width ; the cirrus sockets are in 10 columns which are separated 



by high ridges Stenometra quinquecostata. 



e*. The outer borders of the muscular fossse are convex, more rarely nearly straight, and 

 converge more or less, usually markedly, distally. 

 f. The inner sides of tie interarticular ligament fossfe are straight and run upward 

 and outward at a relatively large angle with the transverse ridge so that the 

 acute distal angle of the interarticular ligament foss.'e reaches a level at or be- 

 yond the halfway point between the inner proximal and distal angles of the nar- 

 row and usually more or less sharply triangular muscular fossffi. 



CHARITOMETRIDiB. 

 ff. The outer borders of the interarticular ligament fossse are very strongly con- 

 cave, so that the interarticular ligament fossse are separated by broadly len- 

 ticular gaps interradially Crinomrtra concinna. 



g'. The outer bor<lers of the interarticular ligament fossse are nearly or quite 

 straight, so that the interarticular ligament fossae are separated by narrow 

 furrows interradially. 

 h\ Muscular fosKP very narrow, about three times as long interiorly as broad. 



Pcecilometra acaela. 

 h'. Muscular fossse wider, about twice as long interiorly as broad. 



i\ Outer border of muscular fossse longer than outer border of interarticular 



ligament fossa; Pachylometra inwqualis. 



i'. Outer border of interarticular ligament fossse longer than outer border of 

 muscular foss:p. 



f. Lines of growth conspicuous Charitometra basuyurva. 



i'. Lines of growth inconspicuous or obsolete Perissometra angusticalyx. 



f. The distal outer angles of the interarticular ligament fossae are never so high above 

 the transverse ridge as the halfway point between the proximal ends and the 

 distal borders of the muscular fossse. 

 g". The height of the articular faces is approximately equal to the length of the 

 transverse ridges, 

 ft'. The muscular and interarticular ligament fossa; are about of the same size, 

 i'. The outer border of the interarticular ligament and muscular fossse com- 

 bined is evenly convex ; the ridge forming the distal border of the inter- 



