142 Transactions of the ' 



described by Gegenbaur,* at Messina, as regards the appendage, 

 but differed from either in the shape of the body. One of these 

 species was named by that author A. acrocerca; this had a tail 

 which was inserted by a thin, short stalk, and terminated in a fine- 

 pointed free extremity. The other he termed A. furcata. In this 

 the tail was inserted by a broad basis, and ended in a forked ex- 

 tremity ; this species also further resembled the subject of the 

 present memoir in having the posterior end of the body also forked. 



The external form of the species I am about to describe is more 

 elongated, and not so compact as that of those animals described 

 by Gegenbaur. From a wide anterior extremity a comparatively 

 narrow neck leads down to a posterior enlargement, which contains 

 such viscera as the creature possesses, and terminates behind in two 

 projecting points. The whole presents a gentle double curve, being 

 convex towards the dorsum at the anterior and posterior end, and 

 towards the ventral surface in the middle. The anterior section of 

 the body is strengthened by thick granular walls, which at the 

 entrance into the pharynx expand into two thick lips, which, being 

 continued by diaphanous material round the circumference, give an 

 appearance somewhat resembling the preoral disk of a rotifer, as it 

 might appear if the cilia were suppressed. The remainder of the 

 body is enclosed in a transparent glassy case of such extreme delicacy 

 that only one specimen out of the number that I examined retained 

 its outline for a sufficient length of time to be sketched, all the 

 others became crumpled up more or less in a few minutes. 



In some cases instead of the anterior extremity terminating in 

 a smooth disk it is prolonged into one or two sharply-pointed 

 curved horns, Fig. 1 ; in others it presents several projecting 

 spikes and prominent ridges. Fig. 3 ; in fact, the shape of this part 

 appeared to vary in every specimen examined, as also did the pro- 

 portions and position of the thick granular walls. The tentacula 

 described by Dr. Moss t were not present in these specimens. 



The pharynx commences as a wide tube behind the preoral 

 disk, and gradually tapering as it passes through the attenuated 

 part of the body it enters a globular thick-walled chamber, which 

 appears to be the stomach ; there is no appearance of a branchial 

 chamber in this animal ; but the whole of the pharyngeal tube is 

 ciliated ; the cilia are more apparent at the posterior end. At the 

 point where the pharynx enters the stomach, a bundle of very long 

 ciha project into the cavity of the latter with a flickering motion ; 

 the rest of its surface is covered by short cilia. Behind, the 

 stomach opens into the side of a larger thick- walled chamber, 

 having its longer axis placed obliquely across the body ; this is the 

 sole representative of the intestine, and opens immediately on the 



* Zeit. f. W. Zool., Bd. 5 and 6, 1854-r)6. 

 t ' Trans. Linn. Soc.,' vol. xxvii., 1870. 



