314 



P. HERBERT CARPENTER. 



Muller are the nearest to the vertical axis of the calyx of all 

 the plates in the interradial areas ; and the term abaxial basals 



Fig. IV.— Dorsal view of one ray of the young Amphiura squaraata; 

 Stage II, after Fewkes. 1. Dorsocentral. 4. Radials. I. Primary inter- 

 radials. i. Other interradials. r. s. Radial shields, am. Ambulacral 

 plates. d v , d„. Upper arm-plates (dorsals). ad y , ad 4 ., ad b . Side arm- 

 plates (adambulacrals). s. Their spines. 



is thus self-contradictory. The proximal ring of interradially 

 situated plates or basals (figs, n, in, 3) cannot be called 

 abaxial; and the interradial plates belonging to a distal or 

 abaxial ring (fig. iv, I) are most certainly not basals. The 

 term adaxial interradials is an expressive (but lengthy) name 

 for the basals (3), as it implies that they lie within the ring of 

 radials (4). But "abaxial basals" as a synonym for the 

 interradial plates (I) beyond this ring is an impossibility; and 

 the use of the term by a trained morphologist like Fewkes has 

 surprised me considerably. 



According to his description 1 the true basals or adaxial inter- 

 radials seem to be the second set of plates to be developed inter- 

 radially in the apical system of the American Amphiura, 

 arising " in the corners left between the dorsocentral and con- 

 tiguous radialia." But before this happens the radial shields 

 and two upper arm-plates have made their appearance (fig. 

 tv, r. s.; d l . d 2 .). At any rate this is how I should interpret 

 Fewkes's fig. 19, which is copied in fig. iv. But it has puzzled 



1 Loc. cit., p. 128. 



