MONOGKAPH OF THE EXISTING CRICOIDS. 



73 



c". The muscular fossa? are at least as large as, and usually much larger than, the inter- 

 articular ligament fossaa. 

 d'. The total height of the articular fossae is much less than the length of the transverse 

 ridge. 

 ('. The distal borders of tlie interarticular ligament fossa run in a broad curve from 

 the distal border of the central canal outward and upward to the distal outer 

 angles of the joint face; as the distal border of the joint face is only slightly con- 

 cave the muscular fossa; are highest interiorly and taper to a point resting on the 

 outer distal angles of the interarticular ligament fossie. 



Comatilia iridometriformis. 

 &. At least the distal half of the outer borders of the joint face is formed by the edges 

 of the muscular fossfe. 

 f. The distal borders of the interarticular ligament fossse are more or less decurved 

 in their outer halves or two-thirds, so that the muscular foss» are higher out- 

 wardly than inwardly; there are no supplementary muscle plates or bosses in 

 the inner proximal angles of the muscular fossse. 

 g^. The muscular fossie are about twice as large as the interarticular ligament 

 fossa?; the distal borders of the interarticular ligament fossfe are very 

 strongly convex; the proximal halves of the muscular foss« are separated 

 interiorly by the distal portion of a broad elevated triangular structure of 

 which the strongly convex base reaches nearly to the central canal, and the 

 distal halves by a narrow space with parallel siAes—Thi/sanometra tenclloides. 

 g'. The muscular fossre are about the same size as the interarticular ligament 

 fossfe; the distal borders of the interarticular ligament fossae are only slightly 

 convex; the joint face elements are separated in the median line by a promi- 

 ment furrow which is more or less constricted between the muscular fossie. 



Leptontmaster venustux. 



f. The distal borders of the interarticular ligament fossae are straight and are usually 



directed more or less upward and outward so that the interarticular ligament 



fossae are triangular and the inner proximal angle of the muscular fossae is 



nearer the transverse ridge than the outer ; a prominent supplementary muscle 



plate or rounded boss occupies the inner proximal angle of the muscular foss.'e. 



ff. The distal borders of the muscular fossae are flattened and nearly parallel to 



the transverse ridge, or convex with the chord of the convexity parallel to the 



transverse ridge; a broadly roundetl outer distal angle is always evident: the 



centrodorsal is well rounded in lateral view Antedon. 



h\ The sides of the intermuscular furrow are parallel, or diverge slightly dis- 

 tally. 

 t". The outer distal angles of the muscular fossfe are very broadly rounded. 



Antedon pctasux. 

 i'. The outer distal angles of the muscular fossie are less broadly rounded. 



Antedon Mfida. 

 Ji'. The sides of the intermuscular furrow converge distally. 

 i\ DLstal border of muscular fossae strongly convex; distal border of inter 

 articular ligament fossae nearly parallel to the transverse ridge. 



Antedon adriatica. 



t'. Distal border of muscular fossae flattened; distal border of Interarticular 



ligament fossie running upward and outward, making a considerable angle 



with the transverse ridge Antedon mediterranea. 



g'. The distal borders of the muscular fossre are very broadly rounded without any 

 indication of a distal outer angle, or slope downward and inward to the end of 

 the Intermuscular furrow; the centrodorsal is a short cyIinder___7';opionien-o. 



