IMONOGRATH OF JAPANESE OPHIUROIDEA. 147 



halves by a series of pores. Three to five arm spmes. One or 

 two tentacle scales to each pore. 



This genus includes Amphmra duplicata Lyman, 1875, A, 

 canescens Lyman, 1879, A. patula Lyman, 1879, A. partita Kœhlee, 

 1897, Ophiadis cUssidens Kœhlek, 1904, and 0. parata Kœhlee, 

 1904, besides the genotype, Amphiactis umbonata Matsumoto, 

 1915. 



The representatives of the present genus were formerly referred 

 to Amphiura by Lyî^ian, and then to Ophiadis by Lütken & 

 MoETENSEN. AmpJiiadis differs from Amphioplus in the absence of 

 the paired infradental papillae, and from Ophiadis in having 

 numerous oral papilloe arranged in a continuous series, so that the 

 oral slits are entirely closed. Further, the internal structures are 

 entirely different from those of the Amphiuridœ. Again, the 

 present genus diflers from Ophiochytra in the well developed radial 

 shields. 



Arnphiactis umbonata Matsumoto. 



Amphiactis umbonata : Matsumoto, Proc. Acad. Nat. Sei. Philadelphia, 

 1915, p. 67. 



Two specimens ; off Misaki, Sagami Sea. 



Diameter of disk 7 mm. Length of arms 30 mm. Width of 

 arms at base 1.2 mm. 



Disk circular, flat, covered with rather coarse and irregular 

 scales. Central plate large, circular, surrounded by ten small scales, 

 corresponding in position to the infrabasals and basais. The five 

 radiais large, larger than the central plate, with strongly curved 

 abcentral border, which almost forms a semicircle. The central 

 and radiais have each a small but distinct central or subcentral 



