106 THE VOYAGE OF H.M.S. CHALLENGER. 



Both Antedon valida and Antedon incerta have a very well-developed anarnbulacral 

 plating on the disk, which extends out on to the arms above the muscular bundles at the 

 sides of the ambulacra, as in many Pentacrinidae, and also over the genital glands. The 

 side plates and covering plates are better differentiated on the pinnules, however, than is 

 the case in that family. In the immature example of Antedon valida, which was obtained 

 at the same station as the two individuals above described, the axillaries and lower 

 brachials are more widely separated and have their sides less flattened than in the adult 

 condition. The basal joints of the first pinnules, however, have their usual appearance, 

 and also those of the distal pinnules- The axillaries are rather hexagonal than triangular, 

 and a considerable portion of the first radials is visible externally, while the arm- 

 joints are relatively longer and more quadrate, as is always the case in young 

 individuals. 



3. Antedon incerta, n. sp. (PL XVIII. figs. 4, 5 ; Part I., ph liv. figs. 6, 7). 



Specific formula — A.—. 



Description of an Individual, — Centro-dorsal bluntly conical, with the upper angles 

 slightly produced. About twenty stout and long cirri, sometimes reaching 50 mm., with 

 nearly seventy joints. The ninth to twelfth are longer than wide, and the following ones 

 gradually shorten and develop a dorsal keel, which is most marked in the middle third. 



First radials barely visible ; the next two somewhat sharply carinate. The axillaries 

 and first brachials with sharp edges and flattened sides. The second and the hypozygal 

 of the third brachial flattened on the inner side only. The junction line of the first two 

 brachials somewhat tubercular. 



Ten arms, of tolerably smooth subtriangular joints, which gradually become quadrate. 

 A syzygy in the third brachial ; the next between the fifteenth and twentieth, and others 

 at intervals of seven to fifteen joints. 



The lower pinnules are stout, with broad carinate joints, diminishing from the second 

 to the sixth brachial and then increasing slowly. The later ones are styliform with the 

 two lower joints slightly expanded. The basal joints of the first pinnule have their 

 outer sides somewhat flattened, and the third, fourth and fifth joints have their inner 

 edges truncated, so as to be flattened against the arm. 



Disk thickly covered with plates which extend out on to the arms at the sides of the 

 ambulacra and also over the genital glands. The pinnules have well-defined side plates 

 and covering plates, most of the former being notched for the presence of sacculi, which 

 are small, but pretty regularly distributed. 

 Colour in spirit, — dirty yellowish-white. 

 Disk about 10 mm.; spread probably about 18 cm. 



