EEPORT ON THE CEINOIDEA. 101 



and come to have a somewhat " wall-sided " appearance. In some species, such as Antedon 

 valida, Antedon incerta, and allied forms, which have large first pinnules, the second 

 brachials that bear them have quite short outer sides which are scarcely flattened 

 at all. But the lower pinnule-joints are extremely modified. Their outer sides are 

 flattened where they meet the corresponding pinnules of adjacent rays, while their inner 

 sides seem to have been cut away so as to let the pinnules lie close against the arm 

 (PI. XV. figs. 5, 6 ; PL XVIII. fig. 5). 



On the other hand, there are some species in which the wall-sided nature of the arm- 

 bases is so comparatively inconspicuous that it might readily escape notice by an un- 

 trained eye. It is a peculiarity which becomes more prominent with age, the radial 

 and brachial joints of young individuals being always longer relatively to their width 

 than in the adult condition, so that those of adjacent rays come less closely into 

 contact. 



This flattening of the apposed sides of the radials and lower brachials is a character 

 which, so far as my knowledge goes, does not appear in any of the Pentacrinidse, though 

 it is very marked in the fossil Solanocrinus costatus, Goldfuss. Quenstedt l figures a ray 

 of this species in which the flattened sides of the syzygial axillaries and of the two 

 lowest brachials are very clearly shown. He says that " von der Seite zeigten nur das 

 erste und zweite Armglied eine breitere Flache, die mit dem dritten pltitzlich schmal 

 wird, und alsdann ganz verschwindet, zum Zeichen, dass mit dem vierten Gliede die Arme 

 schon ganz getrennt waren, und sich mit ihren Innenrandern nicht mehr beruhrteu." 

 In like manner Walther 2 says of the same type " dass, wie bei dem Stiick von Quenstedt 

 die drei untersten Armglieder mit seitlichen Gelenkflachen eng verbunden sind und 

 einen Brachialen Pseudo-heleh bildeten, so dass sich also die Arme erst vom vierten 

 Glied an bewegen konnten." 



In Encrinus and in some species of Apiocrinus this character is considerably exag- 

 gerated, the radials and the lower parts of the arms fitting very closely against their 

 fellows on either side. Traces of it also appear in Holopus, as described on p. 206 of 

 Part I. 



In all but two of the twenty species which belong to the Basicurva-gvoxvp, and have 

 the lower parts of the rays flattened laterally and wall-sided, there are definite covering 

 plates on the pinnule-ambulacra which rest on a limestone band more or less completely 

 segmented into side plates, as for example in Antedon breviradia (PI. XIX. fig. 4). But 

 in two species, Antedon denticulata and Antedon pusilla, there is no ambulacral skeleton 

 at all, a peculiarity which separates them very distinctly from the other members of 

 the group. 



1 Encriniden, p. 174, tab. xcvi. fig. 26a. 2 Loc. cit., p. 171. 



