No. 1G34. AXIAL CANALS OF RECENT PENTACRINITIDJE— CLARK. 91 



circular commissure (figs. 1 and 2) which connects the points of union 

 of the cords received from the basals, around the entire circle of 

 radials. Leaving the radials through a single opening in the distal 

 face, the canal continues undivided through the I Bi^ (figs. 1 and 2) 

 forming a chiasma in the I Br. (axillary), as described by Reichen- 

 sperger. 



In Endoxocrinus parrce (and in E. wyville-thomsoni and E. alter - 

 nicirrus, so far as I can judge from the figures in the Challenger Re- 

 port), infrabasals are absent, and the primary cords pass into the 

 basals by two holes (fig. 14), situated side by side, instead of by one; 

 the course of the canals through the 

 basals, radials, and arms is as de- 

 scribed for Isocrinus decorus and 

 Metacrinus rotundus (fig. 15). The 

 double instead of single entry of the 

 cords into the basals of Endoxocrinus 

 parrce at first sight seems to be a dif- 

 ference of considerable importance; 

 but in reality it has no significance 

 whatever; the infrabasals, present 

 at all stages in Isocrinus decorus and 

 Metacrinus rotundus, are in Endoxo- 

 crinus parrce resorbed at an early 

 age, and, with them, the inner end 

 of the basals; now, as in Isocrinus 

 and Metacrinus the cords fork im- 

 mediately on entering the basals, it 

 is evident that a very small resorp- 

 tion of the end of the basals will 

 result in transforming the single 

 hole into a pair, more particularly 

 since the course of the cords is diag- 

 onally upward, at a comparatively slight angle to the inner surface of 

 the basal (fig. 16). 



A very small specimen of Endoxocrinus parrm with arms only 

 26 mm. long has the infrabasals and interior ends of the basals 

 already resorbed fully as much as in the adult, and has precisely 

 the same arrangement of the axial canals, although the radials, as 

 usual in the young of Isocrinus, Endoxocrinus, and Metacrinus, 

 are much elongated, and the basals (which, as is the case in this 

 species, form a compact closed circle) are very short. 



Fig. 16. — Diagram illustrating the 

 difference in the arrangement of 

 the axial canals between isocri- 

 nus decorus and metacrinus ro- 

 tundus and endoxocrinus parr.e ; 

 the diagram, with the omission of 

 the dotted line, represents the 

 condition in Isocrinus decorus and 

 Metacrinus rotundus; in Endoxo- 

 crinus PARR.E THE INFRABASALS ARE 

 ENTIRELY resorbed, and the basals 



ARE RESORBED AS FAR AS THE DOTTED 

 LINE, WITH A CORRESPONDING IN- 

 CREASE OF THE SMALL CENTRAL AREA. 



