30 MR. G. BUSK ON A NEW POLYZOON. [Jail. 6, 



the front of the larger or hinder one, and about half its length. The 

 external walls of both compartments are very thin and transparent, 

 and marked with fine irregular transverse lines. 



The orifice through which the polypide is protruded appears to 

 belong chiefly, if not entirely, to the smaller compartment, in which 

 may be perceived a dark opaque body probably representing the 

 contracted remains of the polypide, from which in several of the 

 zoocecia the usual contractile, muscular fasciculus proceeds. The 

 two compartments seem to be separated by an obliquely vertical 

 septum, in which may be obscurely perceived a circular opening*, 

 through which the retractile muscle appears to pass to the bottom 

 of the hinder compartment. Besides these structures there may be 

 seen traces of other, probably muscular, bands in the larger compart- 

 ments ; but the whole of the internal economy has yet to be 

 satisfactorily made out. 



In most of the zoocecia the remains of the protruded polypide may 

 still be seen projecting from the apical orifice. I have been unable 

 to discern any fringe of setae, but have no doubt that it will be 

 found that, when the polypide is protruded, its base is surrounded 

 with at least a membranous fringe, as is the case in many of the 

 Ctenostomata. 



Some idea of the appearance presented by the Polyzoon when alive 

 may be formed from fig. 3 in the accompanying Plate, taken from a 

 sketch made by Sir Philip Egerton. From this it would seem that 

 the zoocecium, at any rate on occasion, is capable of being flexed to 

 a right angle upon its peduncle, although in the dead specimen all 

 the zoocecia are continued in a straight line with it. 



For this interesting production I propose the name of Hippuraria 

 egertoni, with the following diagnosis : — 



Suborder Ctenostomata. 



Fam. Hippurariad^e, n. fam. 



Gen. Hippuraria, n. g. 



Stem jointed, nodular, whorls of celliferous tubules arising from 

 the nodes. Zoocecia two-celled. 



Sp. Hippuraria egertoni, n. sp. 



The only species. 



Hab. Berehaven, Ireland (parasitic on Gonoplax angulatus). 



DESCRIRTION OF PLATE V. 



Fig. 1. Hippuraria egertoni, nat. size. 



2. Enlarged about ten times. 



3. Appearance when alive. 



4. Anterior aspect of zoocecium. 



5. Posterior aspect of zoocecium. 



6. Portion of the central stem between two nodes. 



* This opening may probably represent that by which the zoooecia in the 

 other Ctenostomata communicate with the tube from which they spring. 



