1915.] NATURAL SCIENCES OF PHILADELPHIA. 63 



•or less stout, obtuse. Arms composed of rather short and wide 

 joints, uniformly tapered. Dorsal arm plates rhomboidal, with 

 very obtuse inner angle, wider than long, with a more or less distinct 

 median keel, so that the dorsal side of the arm is keeled as a whole. 

 Lateral arm plates with prominent spine ridges, meeting neither 

 Above or below. First ventral arm plate very small, quadrangular, 

 with concave inner side, longer than wide; those following, mod- 

 erately large, pentagonal, with convex, but slightly notched, outer 

 side and rounded outer angles, nearly as long as wide. Six arm 

 spines long, flattened, more or less curved, truncate, translucent, 

 not serrate; uppermost or upper second spine longest, about twice 

 and a half as long as corresponding arm joint; lowest one, shortest, 

 slightly longer than arm joint. Two oval, thin, leaf-like tentacle 

 scales to each pore. Color in alcohol: disk grayish brown, with or 

 without white patches on dorsal side at insertion of arm bases; 

 arms banded with grayish brown and white. The grayish brown and 

 white in alcohol correspond, in life, to dark green and vivid red, 

 respectively. 



Two specimens: off Oshima, Sagami Sea; 75-85 fathoms. 

 OpMothamnus venustus sp. nov. 



This species is very near Ophiomitra habrotata H. L. Clark, but 

 I have some doubt as to the identity of the two species, since certain 

 differences are observable between them as now known. The 

 present species has fine, acute, scattered spines on the disk, without 

 any of the large, conspicuous spines, characteristic of 0. habrotata. 

 The arm spines of the present species are eight to ten in number to 

 each lateral arm plate on free basal arm joints. 



Numerous specimens; off Inatori, Izu, Sagami Bay. 



The internal structure of the present species is quite similar to 

 those of the genotype, 0. vicarius Lyman, the peristomal plates 

 being triple, the genital plates situated above the basal vertebrae, 

 the genital scales absent and the generative glands lined by an 

 unfolded membrane, which contains fine scales, as seen under a 

 microscope. 



The species referred to Ophiothamnus by modern systematists 

 are of a type not considered Ophiothamnus by Lyman, while certain 

 species, which are quite congeneric with Lyman's type of the present 

 genus, have been referred to other genera. For examples, Ophioleda 

 minima and Ophioplinthaca occlusa of Koehler, and Ophiomitra 

 habrotata H. L. Clark, are, in my opinion, genuine Ophiothamnus^ 

 while Ophiomitra exigua Lyman (referred to Ophiothamnus by 



