4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. QI 



jaws is provided with a large broadly rounded triangular papilla. The 

 genital slits are strongly sinuous. 



There are two pairs of tentacle pores, which are completely closed 

 by single large oval tentacle scales situated on the side arm plates. 

 The under arm plates beyond the second pair of tentacle pores are 

 exceedingly minute. 



The first side arm plate beyond the disk bears three short peglike 

 similar arm spines, evenly spaced. The second and following side 

 arm plates bear four, of which the second from the oral side is much 

 stouter than the others, with the inner side strongly convex and a 

 sharp glassy point at the outer side of the distal end. Further out the 

 arm spines become reduced to three, of which the middle one is 

 hooked and curves outward from the arm. and in the outer part of 

 the arm there are only two arm spines, situated close together on 

 about the middle of the side arm plate, the lower very short and of 

 normal form, the upper stouter and hooked. 



OPHIOMUSIUM ALECTO, n. sp. 



Plate 2, figs. 5, 6 



Locality. — Caroline station loo; northeast of Puerto Rico (lat. 

 i8°4o'i5'" N., long. 64°5o'i5" W.) ; 150 fathoms; March 4, 1933. 

 One specimen (U.S.N.M. no. E.5197). 



Description. — The disk is circular, somewhat elevated, 4 mm in 

 diameter, and the slender arms are 10 mm long. 



The center of the disk on the aboral side is occupied by a pentagonal 

 plate with slightly concave sides which is surrounded by a closed ring 

 of five larger seven-sided plates, of which the two distal sides lie on 

 the inner portion of the lower border of the radial shields. In the 

 angles between the plates of this circlet lie pentagonal plates. Beyond 

 each of these pentagonal plates a long plate with slightly diverging 

 sides runs to the edge of the disk and separates the radial shields. 

 The radial shields are separated from the arm bases by a triangular 

 plate not quite twice as broad as long with truncated lateral angles, 

 adjoining which are two small triangular supplementary plates, one 

 on either side. 



The oral side of the disk is covered by a thick skin which more or 

 less conceals the outlines of the underlying plates, even when dried. 

 The mouth shields are five-sided, and about as long as broad. In con- 

 tact with their outer edge is a large trapezoidal plate that occupies 

 the entire space between the genital plates and, turning upward and 

 inward so abruptly as to form a rather .sharp keel, forms the side of 



