1915.J NATURAL SCIENCES OF PHILADELPHIA. 51 



scales. Radial shields rudimentary and insignificant, lying on the 

 disk margin. Genital slits very small and short. 



Oral shields triangular, with convex outer border. Adoral shields 

 large, quadrangular, meeting within. Oral slits short, fairly closed 

 up. Single oral papilla on either side, short, stumpy, conspicuously 

 thorny at tip, turned up ventrally, instead of projecting towards 

 oral slit. Two or three dental papillae at apex of each jaw, similar 

 in shape and in size to oral papilla, also turned up ventrally. Teeth 

 in a single vertical series, stout, stumpy, thorny at tips. Second 

 oral tentacle pores open outside oral slits, each provided with a 

 stumpy and thorny papilla, which arises from adoral shield. 



Arms stout in comparison with the small disk, covered by a thick, 

 naked skin. Dorsal arm plates absent. Lateral arm plates sub- 

 ventral, strongly flaring. First ventral arm plate large, quadran- 

 gular, with rounded angles, slightly longer than wide, much wider 

 without than within; those beyond also large, hexagonal; proximal 

 and proximo-lateral sides very short; distal and disto-lateral sides 

 long; outer angles perfectly rounded; as long as, or slightly longer 

 than, wide, feebly calcified and transparent, except the outer and 

 lateral margins, where the calcification is complete and opaque. 

 Vertebrae short and very stout, with streptospondyUne articulation, 

 the articular shoulder and umbo being very stout, while the articular 

 peg is entirely absent. Arm spines two or three, lying flat on the arm, 

 all converted into compound hooks, hyaline; the uppermost two are 

 subequal, about two-thirds as long as corresponding arm joint, while 

 the lowest one is about half as long as the same. The smaller spines 

 have two or three booklets, which lie in one plane, while the larger 

 ones have six or seven booklets, which lie in two divergent planes. 

 Tentacle pores small, without scales. Color in alcohol: brownish 

 yellow. 



One specimen; Sagami Sea; 300 fathoms. 



Family 2. TRIOHASTERIDJE Doderlein, 1911 (emend.). 

 (Characters as given in key, p. 46.) 



Key to subfamilies of Trichasteridce. 

 A — More than three arm spines; madreporite single, 



ASTERONYCHIN^. 



A A — Two arm spines; all oral shields serving as madreporites. 

 a — Lateral arm plates of opposite sides separated from each 

 other by the ventral arm plates, distal ones projecting 

 ventrally like hanging rods; arm spines subequal; peri- 



