18/4.] MR. G. BUSK ON A NEW POLVZOON. 29 



2. Notice of a New Polyzoon (Hippuraria egertoni) . 

 By George Busk, F.R.S., V.P.Z.S., &c. 



[Eeceived November 26, 1873.] 

 (Plate V.) 



The subject of the present communication is so peculiar in its con- 

 formation and in several respects so widely different from any other 

 Polyzoon with which I am acquainted, that it seems desirable that some 

 notice of it should be placed on record, although I am unable from 

 want of materials to give a full account of its structure. This can 

 only be made out from the examination of fresh or perfect specimens 

 that have been preserved in spirit. 



The only specimen at present available is not sufficient for the 

 purpose, owing to its having been dried and reexpanded. I am 

 indebted for it to Sir Philip Egerton, who discovered the species 

 growing upon the carapace of a Gonoplax angulatus dredged up at 

 Berehaven in the course of last summer. It will, no doubt, when 

 once made known, be found in sufficient abundance ; and the examina- 

 tion of it, in the living or recent state, will well reward the observer. 



The specimen, which is preserved in the British Museum, consists 

 apparently of only a portion of a larger growth. It is about a 5 

 of an inch in length, and consists of a central tubular stem upon 

 which are four nodular enlargements at nearly equal distances apart. 

 From each of these nodes spring on all sides numerous slender 

 transparent tubes, about 0""13 long, each of which supports at the 

 extremity a pyriform zoooecium about "*04 in length. 



The central stem is a hollow, thick- walled, chitinous tube, ob- 

 scurely jointed between the nodosities (Plate V. fig. 2). The latter, in 

 the present condition of the specimen, are quite opaque ; and conse- 

 quently it is impossible to make out their exact relations to the 

 tubular stem, or the precise mode of origin of the celliferous tubules 

 which spring from them. 



The tubules or peduncles, as they may be called, of the zoocecia 

 are slender and very transparent, about ^j of an inch in diameter, 

 and smooth on the exterior. Internally they exhibit what appears 

 to be an irregularly spiral filament ; but the real nature of this 

 structure has yet to be ascertaind. The zoocecia are seated at the 

 extremities of the tubules, to which they appear to be connected by 

 a joint. I have been unable to make out whether there is any 

 communication between the tube and the cavity of the zoooecium. 



The zoocecia or cells are of an elegant pyriform shape, somewhat 

 gibbous on one side, which may be termed the dorsal, whilst on the 

 opposite or anterior the zoooecium at first sight appears to be 

 furnished with a wide aperture closed with a thin membrane similar 

 to that which is met with in very many of the Cheilostomata 

 (as Bicellaria &c), in which area is placed the true mouth with 

 its movable lip. Nothing of the kind, however, appears to exist in 

 Hippuraria ; and the apparent aperture represents the outline of a 

 distinct smaller compartment of the zoooecium, placed as it were on 



