ox DIPLOZOON XIPPONICUM, N*. SP. 153 



has been killed in this way, preserves a natural {xjsition corresponding 

 to its condition of rest, and can be examined when convenietit. 



Each individual, if considered separately, is elongated and lan- 

 ceolate in form, with a deep notch on one side a little posterior to the 

 middle of its winde length, by means of which it is united with the 

 other individual ; so that we may hereafter speak of the anterior and 

 posterior halves of the body. The anterit)r lialf is widest near the 

 place of union, and becomes narrower anteriorly, where it ends with 

 a rounded outline, and where the mouth is situated on the ventral 

 side. In cross-section it presents an oval outline, which gradually 

 becomes more circular as we proceed anteriorly. If the worm has 

 died in a contracted state, the siu'face of the body is thrown into 

 numerous transverse folds ; otherwise the surface is entirely smo<jth, 

 except where little conical elevations, hereafter to be described, exist. 

 The posterior half may briefly be described as an elliptic cylinder in 

 the anterior portion, which, posteriorly, passes irregularly into a rect- 

 angular prism. [t is also much slenderer than the anterior half. 

 Seen in profile, the surface of the posterior portion is always, in 

 specimens killed with hot sublimate, thrown into a number of strong 

 folds, due no doubt to the powerful development of the diagonal 

 muscular libres in this region ; so that here the margin is deeply 

 crenate or even zig-zag (PI. XXI, Fig. I). A cross-section through 

 one of the posterior zig-zag folds presents nearly a rectangular out- 

 line. The folds suddenly come to a close at a short distance before 

 the beginning of the posterior suckers. In this portion the crcjss- 

 section presents a flattened ellipse ; and this part is, on surface view, 

 distinctly marked off from the sucker-bearing portion which directly 

 follows it, and still more so from the strongly folded more atiterior 

 portion, by a sudden change of level (Fig. 1). The lateral margins 

 of this sucker-bearing portion are suddenly thickened on the ventral 



