678 RHABDOPLEURID^E. 



a distinct Subclass, we have an account from Allman and 

 from G. O. Sars: the former has studied our British JR. Nor- 

 mani ; whilst the latter has given us an exhaustive memoir 

 on a Scandinavian species, R. mirabilis, founded on a care- 

 ful examination of living specimens. The most significant 

 peculiarities of Rhabdopleura are the structure of the 

 lophophore and the disposition of the tentacles upon it. 

 Instead of a circular or crescentic stage round which the 

 arms are ranged in a continuous series, we have here two 

 long and narrow and more or less divergent lobes, ex- 

 tending out from the anterior region of the body in a 

 dorsal direction, and each bearing a double row of ten- 

 tacles. The tentacular wreath has disappeared ; and in 

 its place we have two independent tentaculiferous pro- 

 cesses, which are highly flexible and mobile, reminding 

 us more of the " gill-tentacles " of Terebratula than of 

 the lophophore of the ordinary Polyzoa. 



Another striking feature of the present form is the 

 large shield-like organ (" buccal shield "} situated be- 

 tween the two orifices of the alimentary canal, which is 

 probably the homologue of the Molluscan foot' 5 *'. Ac- 

 cording to Sars's observations, it is by means of this 

 organ (in the absence of all protrusor muscles) that the 

 polypide slowly draws itself up to the mouth of the 

 cell. 



* Allman, indeed, takes a different view of this organ, based chiefly on 

 observations made on the early development of the polypide, and is inclined 

 to compare it with the mantle of a Lamellibranchiate mollusk. His account 

 of the evolution of the bud I am unable to follow so as fully to appreciate 

 its bearing on the point in question ; but there seem to me to be serious 

 objections to the proposed interpretation. Sars regards the shield as the 

 equivalent of the epistome of the Freshwater Polyzoa ; and Prof. Ray 

 Lankester identifies it with the Molluscan foot, conclusions in which (with 

 our present knowledge) I fully concur. 



