162 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



in the proximal portion of the arms, and at certain places these 

 plates are in contact; it is only at a considerable distance from the 

 disk that they become separated by a narrow interval. 



The upper arm plates are not very broad, and the first plates, 

 especially, are narrower than those following, a character which 

 separates A. vadicola from another very closely related Japanese 

 species, A. aestuarii Matsumoto. The arms are in fragments, and it 

 is difficult to estimate their length, but they may easily be thirty 

 times the diameter of the disk, corresponding to the figure given by 

 Matsumoto. 



The spines are covered with asperities throughout almost their 

 entire length, and especially at their tips; they are more or less flat- 

 tened and subequal, but the second acquires, at some distance from 

 the disk, a quite characteristic form (pi. 96, fig. 5a). It is at first 

 rather broad and flattened, then, after tapering very gradually, it 

 broadens abruptly into a sort of disk of which the width equals 

 almost that of the basal portion of the spine, and which is covered 

 with short and closely crowded spinules. This tip thus resembles 

 the rowel of a spur, and this form justifies Matsumoto's comparison 

 when he says that the second spine is " spur-shaped." 



A species closely related to A. vadicola has been recently described 

 by H. L. Clark under the name of A. ecnomiotata ('11, p. 148), from 

 a single specimen found at a littoral station in Japan, but it is very 

 distinct from A. vadicola. Another Japanese species, also described 

 by H. L. Clark, is A. acrystata, which is especially interesting because 

 it shows that the principal character upon which the old genus 

 Ophionephthys was based is essentially variable. In certain speci- 

 mens (H. L. Clark '11, p. 146, fig. a) the plates of the dorsal surface 

 of the disk are localized about the periphery of the radial shields, 

 leaving the rest of the surface of the disk naked, while in others this 

 border of plates broadens (fig. d), and sometimes it even covers the 

 entire dorsal surface of the disk (fig. g) . 



Matsumoto has suggested the advisability of suppressing the genus 

 Ophionephthys and including it in the genus Amphiura, and I hold 

 absolutely the same opinion. I have already had occasion to remark 

 recently, in describing Amphiura latispina ('14, p. 50), that the dor- 

 sal plates of the disk in that species show the arrangement which 

 authors consider characteristic of the genus Ophionephthys, but I 

 have thought it necessary nevertheless to retain it in the genus 

 Amphiura. 



Matsumoto's memoir of 1917 includes figures of Amphiura 

 aestuarii (p. 209, fig. 57) and of A. vadicola (p. 211, fig. 58), and I 

 have been able by comparing the Albatross specimens with these to 

 confirm my determination; thev are without doubt A. vadicola. 



