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



type. There is a further resemblance between Antedon basicurva and the mature 

 Antedon breviradia, in the presence of transverse ridges and furrows at the lower ends of 

 the muscle-fossee (PL II. fig. 2<x ; PL III. fig. 46). I have found two radials without 

 them, however, in one calyx of Antedon basicurva. 



Some of the individuals of this species, including the youngest one above mentioned, 

 are deformed by the cysts of Myzostoma willemoesii, and Myzostoma tenuispinum, von 

 Graff. 



14. Antedon incisa, n. sp. (PL II. figs. 1, a-d ; PL XXI. figs. 1, 2). 



Specific formula — A.—. 



Centro-dorsal hemispherical, with a rough dorsal pole and small interradial processes. 

 About fifteen cirri of some fifteen to eighteen rather stout, smooth joints, most of which 

 are longer than wide. In the younger cirri the later joints overlap very slightly on the 

 dorsal side so as to produce faint spines ; this is lost in the older cirri, except in the 

 penultimate, which bears a strong opposing spine. 



Three radials visible ; the first short and band-like with curved borders, meeting one 

 another above the interradial processes of the centro-dorsal ; the second somewhat longer, 

 in close lateral contact, and rather convex in the centre, but little incised for their 

 junction with the axillaries, which are also sharply convex, short and pentagonal, with 

 very open angles. The axillaries and the first four or five brachials have the marginal 

 portions of their dorsal surface flattened vertically, with sharp edges and wall-like sides. 



Ten arms ; the first brachials almost oblong, and very convex in the centre ; the second 

 shorter and more wedge-shaped. The following joints smooth and rather short till about 

 the tenth, then longer and obliquely quadrate, becoming blunter and more elongated 

 towards the end of the arm, but without any overlap. 



A syzygy in the third brachial ; the next frequently in the tenth, but sometimes not 

 till the eighteenth ; and others at intervals of one to nine, generally four to six, joints. 



The second brachial has a longish pinnule of about thirty short joints, the lower ones 

 rather flattened on the outer side with a sharp dorsal keel. A similar but shorter pinnule 

 on the third brachial. The next pinnule is longer, with fewer but larger joints, the 

 fourth and fifth of which are broad and expanded towards the ventral side. The 

 expansion increases in the following pinnules, which have the third and fourth joints 

 largest. This is most marked about the twelfth, but is traceable nearly to the thirtieth 

 brachial. The remaining pinnules diminish in stoutness without increasing much in length. 



Disk much incised and pretty completely plated, as are also the brachial ambulacra. 

 The genital glands protected by stout anambulacral plates. The ambulacra of the distal 

 pinnules have well-marked side plates, which are generally notched for the sacculi. 

 These are large and abundant, especially on the genital pinnules. 



