NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 273 



spines. Upper arm plates wanting. Teeth spiniform in a double 

 series, followed by a few tooth papillae ; oral papillae reduced to a few 

 tubercles. Under arm plates present. Arm spines rough and skin- 

 covered. Tentacle scales wanting. 



Type-species, Ophiophrixus acanthinus. 



Although this genus has the form and general appearance of Ophio- 

 myxa, it is evident from the mouth parts that it is not really very 

 nearly related to that group. The notable radial shields and the 

 absence of upper arm plates are further obvious, but not so essential, 

 differences. 



OPHIOPHRIXUS ACANTHINUS, new species.^ 



Disk 12 mm. in diameter; arms about 80 to 85 mm. long. Disk 

 covered with a thin skin carrying, near center, a few scattered scales, 



FIG. 137. OPHIOPHRIXUS ACANTHINUS. x 4. a, FROM ABOVE; 6, FROM BELOW; c, SIDE VIEW OF TWO 



ARM JOINTS NEAR DISK. 



each of which bears a minute spine. Radial shields narrow, and com- 

 pressed into a distinct ridge, well separated, parallel; each one carries 

 six or seven erect, acute spines. Between distal ends of radial 

 shields of each pair are two large calcareous plates in contact with 

 each other. Upper arm plates wanting, but arm bones show through 

 thin skin of arm. Interbrachial spaces below naked. Genital slits 

 large. Oral shields rather large, triangular, with curved lateral mar- 

 gins, about as long as wide. Adoral plates large, much broader 

 without than within where they meet. Jaws very short, each with 

 a double series of rough spiniform teeth, below which, at apex of 

 jaw, are four or five small, blunt tooth papillae, irregularly arranged; 



f, signifying thorny, in reference to the appearance of the arms. 

 34916 Bull. 7511 - 18 



