88 PROCEEDINGS OF THE ACADEMY OF [Feb., 



dorsal median ridge, triangular in transverse section. Dorsal arm 

 plates large, occupying almost entire dorsal surface of arm, quad- 

 rangular, with rounded outer corners, a little wider without than 

 within, three to four times as wide as long, with a rather sharp ridge 

 on the median line; some are divided into several irregular secondary 

 plates. Lateral arm plates very low, less than half height of arm, 

 meeting neither above nor below. Ventral arm plates small, rhom- 

 boidal, with shorter diameter parallel to arm axis. First plate 

 almost as wide as, but much shorter than, following; the three or 

 four plates beginning with the second have a median keel, which is 

 more prominent proximally both with regard to each plate and to 

 the arm as a whole. Arm spines four for the most part, but three 

 distally, very short, flattened, lanceolate, obtuse, lowest one some- 

 what longer than the others, but not so long as corresponding 

 arm joint. One tentacle scale, large, oval, thin, flat. Color in 

 alcohol: light yellowish brown. 



Two specimens; Sagami Sea, 170 fathoms. 



This new species is very near B. lacerlosa (Lyman), but differs 

 from it in the coarser disk granules, in the smaller naked part of the 

 radial shields, in the more strongly ridged dorsal arm plates, in the 

 much lower lateral arm plates, in the wider and rhomboidal ventral 

 arm plates, and in the shorter arm spines. 



Family 4. OPHIOCHITONID.E nov. 

 (Characters as given in keys, pp. 74 and 75.) 



Key to subfamilies of Ophiochitonidoe. 



A — Teeth triangular, not very stout; peristomal plates moderately 

 large; oral frames entire, without well-developed lateral wings; 

 dorsal side of vertebrae entire, rhomboidal Ophiochitonin^. 



A A — Teeth c^uadrangular, very stout; peristomal plates very small; 

 oral frames with well-developed lateral wings; dorsal side of 

 vertebrae notched inwards and V-shaped Ophionereidin^. 



Subfamily 1. OPHIOCHITONIN^ nov. 



(Characters as given above in key.) 



This subfamily includes Ophiochiton^ and Ophioplax. 

 OpMoplax lamellosa sp. nov. 



This new species is quite near Ophioplax Ijungmani, Ophiopeza 

 custos Koehler (referred to Ophioplax by Koehler) and Ophiopeza 



^Ophiocfdlon lymani Studer, 1883, is, in my opinion, referable to Ophiocten, 

 being allied to Ophiocten hastatus Lyman, 0. pacificiim Liitken and Mortensen, 

 etc. 



