14 ART. 2. — H. MATSUMOTO : 



with acute tips. Dental papillsG absent. Second oral tentacle pores 

 opening entirely within the oral slits. Yertebrse more or less 

 divided into halves by a longitudinal fusiform pore in the outer 

 half of the arm. Dorsal arm plates entirely absent, lateral arm 

 plates more or less subventral in position, so that the dorsal side 

 of the arm is mostly unprotected. Two or three arm spines, all 

 converted into compound hooks. Tentacle scales absent. 



This genus differs from Ophloscolex cliiefly in the presence 

 of the marginal disk scales and in the conversion of the arm 

 spines into compound hooks ; and from Neoplax in the fewer arm 

 spines, wliicli are all converted into compound hooks, and in the 

 absence of the tentacle scales. 



OpJiiostiba hidekii Matsumoto. 



Opliiostiba hideJcii : Matsumoto, Proc. Acad. Nat. Sei. Philadelphia, 

 ILXyn, 1915, p. 47. 



Two specimens ; Mera-out-Oisegaké, Sagami Sea ; 300 fathoms. 



Diameter of disk 3.5 mm. Length of the longest arm 1(3 mm. 

 Width of the same at base 0.8 mm. 



Disk hexagonal, with concave interbrachial borders, ratlier 

 convex dorsally, covered by a soft skin, wliich contains fine, 

 scattered, calcareous granules. Marginal disk scales present, but 

 rudimentary, liable to be overlooked. Eadial shields very rudi- 

 mentary, insignificant, forming a continuous row with the marginal 

 disk scales. Genital slits very small and short. 



Oral shields rhomboidal, with perfectly rounded outer and 

 lateral angles ; convex, slightly longer than wide ; all serving as 

 madreporites. Adorai shields narrow, but with widened outer end, 

 wliich entirely sejoarates • the oral shield from the first lateral arm 

 plate ; adradially concave, meeting each other within. Four or 



