24 Rev. T. Hincks on the 



give it a pretty speckled appearance ; orifice arched and ex- 

 panded above, more or less narrowed downwards, contracted 

 by a small acute projection on each side just above the lower 

 margin, which is distinctly curved ; peristome not raised. 

 Avicularia keyhole-shaped, placed on a distinct area, very 

 much smaller than that of the cell, sometimes immediately 

 above a zooecium, more commonly in the angle between two 

 zooecia ; mandible directed upwards. OcRcium (fig. 2 a) very 

 large, higher than broad, depressed towards the opening, and 

 often grooved longitudinally above the oral arch, rising above 

 into a kind of central knob (but on the whole not much ele- 

 vated), white, glossy, thickly punctured. 



Zoarium forming large, spreading, whitish crusts. 



Houston-Stewart Channel ; Cumshewa, 20 fms. 



Cases occur in wdiich the avicularium is situated on an area 

 almost as large as that of the cells, just below the upper 

 extremity, occupying, in fact, the position of the oral aperture. 

 Occasionally two of these appendages occur together, either 

 placed one above the other or side by side. 



POEELLA, Gray. 

 Porella concinna^ Busk. 



Cumshewa, on shell. 



[Britain, Adriatic, Finmark, Norway, Spitzbergen, Franz- 

 Josef Land [Ridley), Greenland, Gulf of St. Lawrence, 

 Bass's Straits.] 



A beautiful variety occurs in which the whole surface of 

 the cell, except the umbo below the orifice, is covered with 

 rather large punctures ; the orifice is amj^le, and its characteristic 

 features are very distinctly marked. The zoarium is white, 

 and delicate in texture. 



Porella marsupium, MacGillivray, form porifera. 

 (PI. IV. fig. 4.) 



This species, which is a common Australian form, occurs 

 abundantly amongst the dredgings. The specimens from the 

 Queen Charlotte Islands differ from those which I have exa- 

 mined from Bass's Straits in one or two points, but they are 

 quite unimportant. On the front of the suboral swelling, 

 which supports the avicularium, are two (or occasionally three) 

 rather large circular pores, placed side by side. They give 

 a somewhat peculiar appearance to the cell, but do not seem to 

 have any special significance. Frequently too there is a 

 small raised oval avicularium on the front of the cell, besides 



