1915.] NATURAL SCIENCES OF PHILADELPHIA. 67 



triangular, with pointed ends; dental papillse absent. Peristomal 

 plates large, entire. Oral frames long and slender in internal view, 

 without well-developed lateral wings. Vertebrae of distal arm joints 

 often incompletely divided by a series of pores. Arm spines few. 

 Tentacle scales present, one or two to each pore. 



This genus includes Amphiura canescens, duplicata, and patula 

 of Lyman; Amphiura partita, Ophiactis dissideris and 0. parata of 

 Koehler, besides the genotype, Amphiadis umbonata sp. nov. 



Certain representatives of the present genus were referred to 

 Amphiura by Lyman, and then to Ophiactis by Liitken and Mor- 

 tensen. Amphiadis differs from Amphiura and its allies in the 

 absence of paired infradental papillae, and from Ophiadis in the more 

 numerous papillae, which are arranged in a continuous series so as to 

 close the oral slits. Further, the contrast of the present genus and 

 the Amphiuridm in many internal structures is decidedly striking. 

 Amphiadis much resembles Ophiochytra, especially 0. tenuis Lyman, 

 but differs from it in the well -developed radial shields. 

 Amphiactis umbonata sp. nov. 



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, irregular scales, among which the primaries are distinct. 

 Central plate large, circular, encircled by ten small scales, which 

 correspond to infrabasals and basals in position. Radial plates 

 large, larger than central plate, with strongly curved outer border, 

 which almost forms a semicircle. The central and radial plates 

 have each a small but distinct central boss. The second radials and 

 the first to third interradials may also be distinguished, being larger 

 than the secondary scales, which are irregular in size and in arrange- 

 ment. Thus, the disk squamation is rather similar to that of 

 Ophiozona. Radial shields comparatively small, oblong ovate, about 

 two-fifths as long as disk radius, twice as long as wide, wider without 

 than within, more convex abradially than adradially, separated by 

 a row of three or four plates, of which the inner ones are larger than 

 the outer. In each interradial area there are five to seven irregu- 

 larly radiating rows of scales. Ventral interbrachial areas covered 

 with more or less coarse, irregular scales. Genital slits long, nearly 

 reaching disk margin. Genital scales invisible in external view. 



Oral shields small, rhomboidal, with acute inner angle, lateral 

 and outer angles rounded, inner sides slightly concave. Adoral 

 shields quadrangular, wider without than within, nearly or quite 

 meeting within. Four oral papillae on either side, inner ones smaller 



