280 bulletin: museltm of comparatH'E zoology. 



there were only 3 arm-spines, the upper arm-plates were three 

 times as wide as long and broadly in contact, and there was a distinct 

 tentacle-scale. There is little reason to doubt that Bell's specimens 

 are Amphiuras but the species certainly cannot be determined from 

 the data published. 



The six species of Ophionephthys which seem to be valid may be 

 distinguished as follows : — 



Key to the Species of Ophionephthys. 



a Arm-spines on basal arm-segments not more than 5. 

 b Upper arm-plates narrow, not twice as wide as long. 



c Oral shields longer than wide; usually 2 or 3 small, distal oral papillae; 



usually a single small tentacle-scale limicola 



c' Oral shields wider than long; 1 distal oral papilla, or rarely 2; no 



tentacle-scale phaleraia 



b' Upper arm-plates twice as wide as long aestuarii 



a' Arm-spines on basal arm-segments, 7-10. 



& Upper arm-plates twice as wide as long vadicola 



b' Upper arm-plates much longer than wide. 



c Distal oral papilla more or less cylindrical or terete; arm-spines, 8-10 



ecnomiotata 



c' Distal oral papilla, flat and scale-like, though thick; arm-spines, 



• 7 or 8 odacantha 



Ophionephthys limicola. 



Liitken, 1869. Add. ad hist. Oph., pt. 3, p. 24, 25, fig. 



No specimens with disks are accessible but according to Liitken's 

 figure there is a well-marked marginal series of scales across the 

 interradii. This does not occur in any other species of the genus. 

 The number and arrangement of the oral papillae is peculiar, for each 

 oral plate bears two, rarely one or three, very small, blunt papillae 

 and there is no large papilla on the adoral plate or near its junction 

 with the oral plate. The pair of block-like papillae on apex of the 

 jaw is conspicuous. In all three of the cotypes in the M. C. Z. collec- 

 tion, there is nearly always present a minute tentacle-scale either on 

 the side arm-plate or in the angle where this plate joins the under 

 arm-plate. So far as I can ascertain this species had not been met 

 with since its original description, until in June, 1917, two specimens 



