Manchester Memoirs, Vol.xlii.{\ZgZ\]Slo.V^, 7 



or even two, whilst not one of the remaining zooecia of 

 the colony bear any. 



In one or two cases, knobbed cells are seen {^Fig. i,^), 

 which are characteristic of the British species {see Hincks, 

 Brit. Mar. Polyzoa, p. 307). I have seen no trace of an 

 ovicell. 



Porella tridentata, sp. nov. 



Zooecia hexagonal, separated by fairly deep linear 

 furrows ; surface convex and punctured by large irregular 

 pores which, in some cases, are definitely arranged round 

 the margin. 



Secondary orifice horse-shoe shaped or inversely 

 subtriangular, with a lateral raised collar meeting in a 

 sudden depression behind {^Fig. 4, b), often a sinus in front, 

 containing a small avicularium with a rounded mandible 

 {Figs. 4 and 5, b). In many cases a spatulate avicularium is 

 present to the right of the secondary orifice (Figs, a, and 5,<^). 



Deep down in the orifice can be seen a large median 

 denticle with two lateral ones {Figs. 4 and 5, c and d) ; 

 because of this feature it has been thought fit to call the 

 species " tridentataJ' 



The ovicell {Fig. 5, Ov.) is semicircular in outline, 

 convex in front, somewhat granular, with one or two groups 

 of irregular punctures. 



Zoarium encrusting shell {Photinula violacea) and of a 

 dirty pink colour. 



Porella trideiitata is somewhat like P. concinna (Hincks, 

 Brit. Mar. Polyzoa, p. 323). It differs from the latter in 

 having two lateral denticles in addition to the median one 

 which is present in P. concinna. It is also somewhat 

 larger, and the pores are bigger and irregular in shape. 

 The spatulate avicularium appears to be constant in posi- 

 tion, while the general shape of the secondary orifice seems 

 to be somewhat different. 



