100 



THE VOYAGE OF H.M.S. CHALLENGER. 



The first of these groups to be considered is one which has hitherto been entirely 

 unknown to me except in fossil Coruatulae, and therefore consists entirely of new species 

 discovered during the cruise of the Challenger. I will call it the Basicurva-grou]), for 

 it is in Antedon hasicurva that its principal distinctive characters are, on the whole, 

 most clearly visible. 



In all the species of this group not only the two outer radials, but also the lowest 

 brachials of adjacent rays, come into very close mutual apposition, so that their sides are 

 flattened against one another. 1 



Fig. 2, A, represents a calyx of Antedon hasicurva from which three rays have been 

 entirely removed ; and it then appears that the two lateral faces of each pair of outer 



Fig. 2. — Antedon hasicurva, x 3. A. Side view of the calyx and arm-bases after the removal of three rays, so as to show 

 the sides and inner faces of the other two. The two outer radials, two lower brachials, and in a less degree also the 

 third and fourth, have their outer sides flattened against one another. The genital pinnules have the third and fourth, 

 and sometimes the fifth joints greatly expanded, but the following ones are smaller. B. The lower part of an arm from 

 its inner side, to show the flattened inner faces of the first three brachials, including both the hypozygal and the 

 epizygal of the third. 



radials are quite smooth and flat, like those of the first radials at the bottom of the 

 calyx, and they are in close apposition with those of the second and axillary radials in 

 adjacent rays. In like manner the outer faces of the first brachials on adjacent rays 

 come into close mutual contact and are very perceptibly flattened. The same is true of 

 the second, and in a less degree also of the third brachials, all these three joints being 

 somewhat compressed laterally, with flattened sides and sharp, straight, outer edges. 

 The inner edges and sides of the second and third brachials present the same feature, as 

 seen in fig. 2, B, so that the lower portions of the arms lose their usual rounded character 



1 This character is more or less distinct in some forms of Antedon milberti, but appears to be a varietal rather than 

 a fundamental one (see p. 197). 



