PORELLA CONCINNA. 323 



Our only alternative would be, whilst grouping in the 

 same family all the forms with kindred zooecia, to found 

 genera for the more striking variations of growth, as well 

 as for the more important modifications of the cell. But 

 as our object in classification is merely to indicate, as far 

 as possible, natural affinities, we shall attain our end 

 equally, and with more convenience, it seems to me, by 

 the course which is here adopted. 



a. Zoarium incrusting. 



PORELLA. CONCINNA, Blisk. 

 Plate XLVI. 



LF.PRALIA CONCINXA, Bust, B.M. Cat. ii. 67, pi. xcix. : Hincks, Deyon and 

 Cornw. Cat., Ann. N. H. ser. 3, ix. 201 (41 sep.). 



LEPRALIA APERTA, Boeck, Forh. Vid. Selsk. Christiania, 1861, 50. 



PORELLA L.EVIS, Lepralise auctt. forma, Smitt, CEfv. K. Vet.-Ak. Forh. 

 1867 (Bihang), 21 and 134, pi. xivi. figs. 112-119. 



LEPRALIA BELLI, Dawson, Rep. GeoL Surv. Canada, 1858, 256. 



Zooecia ovate or rhomboid, slightly convex, granular, 

 often punctured round the margin, disposed in lines ; 

 orifice (adult) arched above, contracted below, longer 

 than broad, lower margin straight, the cell-wall fre- 

 quently raised and thickened round the mouth, a broad 

 denticle set rather deeply within it ; oral spines two ; a 

 small avicularium, with rounded mandible, on the lower 

 lip, the front of the cell immediately below it often 

 more or less mamillated. Ocecia globose, prominent, 

 minutely granular, sometimes a single, central puncture 

 in front ; fertile zooecia much raised and swollen to- 

 wards the orifice *. 



* They are so much elevated and enlarged towards the oral region that 

 they appear as little hillocks studding the flat surface of the zoarium. 



