﻿XII. 



On a New Species of Medusa related to Stephanomia, Crystallomia tolygonata. 



By JASIES W. DAjS'A. 



The species here described was taken by the writer in the Pacific, in lat. 30° N. and 

 long. 179° E., on the 24th of May, 1841. 



The animal is nearly colorless and transparent. Length, 4 inches ; diameter, 1-1^ 

 inches. The body is naturally divided into an anterior and posterior portion, the 

 former polygonally ovoid, the latter subprismatic, a little tapering. 



The pieces or blocks of the posterior portion are thin wedge-shaped (Fig. B), and 

 lie in two longitudinal series, facing in opposite directions, the blocks of the two over- 

 lapping and alternating with one another. Together they give to this part of the 

 body approximately the form of a "six-|ided prism, with the sides slightly concave. 

 From the position of the mouth, two of these sides may be called the dorsal, and two 

 the ventral ; the two lateral consist each of two longitudinal planes, owing to a slight 

 angle along the medial line. 



The angle between the two dorsal surfaces, and also that between the two ventral, 

 is truncated ; and at this place in each block there is a circular aperture closed by a 

 valve opening into a sac situated transversely Avithin the block or piece (Fig. B). 

 The valve was in constant action when the animal was first taken. A slender vessel 

 runs inwardly from the sac through the block, perforating its inner or thin edge, show- 

 ing the existence of a kind of aquiferous system in the animal. 



The blocks constituting the ovoidal or anterior portion of the animal are of very 

 different shape from those of the posterior part, as seen in Fig. C ; and they are so 

 arranged together as to give the ovoid a series of narrow longitudinal faces a little 

 concave. They are like quadrangular wedges, thinning from one angle to that diago- 

 nally opposite, and having the two outer faces divided vertically into two concave faces. 

 These blocks are so set together that one series corresponds to the angles, and another 

 to the faces, of the hexagonal prism of the posterior portion of the body. 



The ovoidal anterior portion has a long longitudinal opening on one side, at the inner 

 part of which, just below the medial line of the body, there is a large number of ten- 

 tacles surrounding the mouth, and small red clusters of retracted nettliug-filamcnts. 



