32 GEORGE OSSIAN SARS. 



form of this disc is, as above mentioned, oval, or rather, 

 rounded pentagonal (see fig. 2, c), nearly half as long again 

 as wide, the width about equal to that of the body at the be- 

 ginning of the stomach. Its posterior border, which at 

 once shows itself separated by a deep constriction from 

 the part of the body lying behind it, is in the middle slightly 

 incurved (fig. 3). The side borders are, a little in front of 

 the middle, strongly, almost angularly bent, and then con- 

 verge strongly towards the anterior freely projecting extre- 

 mity, which is narrowed obtusely. The whole disc is every- 

 where, and especially distinctly on the edges, thickly covered 

 with small vilDratory cilia. Allman, who also mentions this 

 prominence, but without having gained a correct notion of 

 its form and connexion with the other parts, says of it that 

 one might take it for a large and peculiarly developed epi- 

 stome, if its position on the ventral side of the mouth, and 

 not, as in the freshwater Polyzoa, between the mouth and 

 the anus, did not oppose such a supposition. Allman sup- 

 poses, thus, that the mouth in the Rhabdopleura, in analogy 

 with the other Polyzoa, is terminal, and situated above or on 

 the dorsal side of this prominence, between it and the anus. 

 Such is, however, not the case. The anterior extremity of 

 the body above the prominence described is completely closed, 

 without any ti'ace of aperture (see fig. 4). On the other 

 hand I have, by gently compressing the animal, been able 

 distinctly to see (see fig. 1) that the buccal aperture (q) is 

 situated just on the ventral or haemal side behind that promi- 

 nence, and seems to have the form of a cross slit, which is 

 bordered behind by an oval lobe (m), furnished with vibratory 

 cilia like a sort of underlip. By increased pressure the 

 buccal shield could be moved more out from the base of the 

 tentacular arms, and it appeared then everywhere very dis- 

 tinctly constricted from the rest of the body, and in the middle 

 of the dorsal surface fixed to the body by a sort of short stalk, 

 while the upper and the lower parts were free. Further, it 

 was observed that on each side of the buccal shield there ex- 

 tended, from the base of the tentacular arms downwards, a 

 strongly projecting nearly semilunar border of thin skin (1), 

 ciliated on its edges, so that between this and the buccal 

 shield there is formed on each side a narrow half-tube or 

 channel leading to the buccal aperture, and through which 

 the nourishment is probably conveyed to the mouth by the 

 abundantly ciliated tentacles. Since, as above stated, the 

 said buccal shield is really situated between the mouth and 

 the anus, I think we may consider it as morphologically 

 answering to the so-called epistome in the fresh water 



