110 ME. P. H. CAEPEXTER ON THE GENUS ACTINOMETEA. 



the analogies of Aj^iocriinis and Eugeniacritms, strengthen Pourtales's view still more 

 completely. 



The occasional fusion of the upper stem-joints with the lower part of the calyx, as 

 descrihed above in the Apiocrinidce, is an excellent illustration of Miiller's idea respecting 

 the correspondence between the basis and the stem-joints. 



This correspondence, however, is by no means entitled to rank as a serial homology. 

 The earliest condition of the basals shows them to be live separate plates developed in a 

 spiral around the aboral ccelom of the Crinoid embryo'. They have distinct homologies 

 in the apical system of the other Echinoderms- ; while the stem-segments, surrounding 

 the aboral ccelom much in the same way as the basal circlet, are simple undivided pieces 

 from the first, and seem to be almost or quite unrepresented in the other Echinoderms. 



(vi.) The Second and Third Radials. 



(§ 74) The second radial oi Act. polymorph a (PL VII. fig. 2), like tliat oi Ant. rosacea, 

 is an oval, somewhat discoidal plate, having two nearly parallel faces — one internal or 

 proximal, articulating Avith the first radial, the other external or distal, articulating with 

 the third radial. The internal face (fig. 2 a) closely resembles the external face of the 

 first radial (PL VII. fig. 1 b), with which it articulates, being divided transversely by a 

 large articular ridge (i) into a dorsal and a ventral portion ; the former is entirely occupied 

 by the fossa lodging the elastic ligament {j), which is particularly deep just below the 

 opening of the central canal {c.c). Erom the ventral margin of this opening arise 

 the two ridges which bound the intermuscular fui'row {fi), and are joined near their 

 upper extremities by the transverse secondary ridges separating tlie lai'ge fossae (A) 

 that lodge the interarticular ligaments from those {/) lodging the flexor muscles of the 

 ray ; the latter arc excavated in a pair of thin lamelte, which extend upwards from 

 the proper ventral margin of the plate, as is seen in a view of the distal face (fig. 2 b, 

 y). Besides the above-mentioned ridges and fosstc, which correspond to similar ones 

 on the distal face of the first radial, the proximal face of the second radial shows two 

 lateral processes, in which shallow fossae (A;) are excavated. These processes represent the 

 outer portions of the distal face, which is somewhat wider than the proximal one, as the 

 lateral faces are not set at right angles to the two terminal ones, but form an oblique 

 angle with tlie proximal face, so that the outline of the radial, when seen from the dorsal 

 or ventral side, is trapezoidal in form (fig. 2 c, d). The shallow fossic which are exca- 

 vated ill these lateral faces lodge the ligamentous substance by which the second ladials 

 are united with one another in pairs : the extent of this union is, as above remarked, 

 very variable in different specimens, being generally greatest where the number of arms 

 is largest (PL II. figs. 9, 11). 



The external or distal face (fig. 2 b) is much simpler in character than the proximal 

 one, as no muscles arc attached to the vertical lamelhc which rise from its ventral 

 margin above the articular face proper. This last is divided by a vertical ridge (/) that 



' Gfittp, he. cit. pp. 595, G20. 



■ V. H. Carpenter, " On the Oral and Apical Systems of the Echinoderms," Quart. Journ. Micr. Sci. xviii. (1S7&) 

 pp. 371, 3^2. 



