352 ESCHARIDiE. 



the cell rises markedly towards the mouth, and the front 

 of the peristome is thus elevated, while the upper mar- 

 gin appears depressed. In S. cheilostoma the surface is 

 level and uniform, and the margin as much elevated above 

 as in front. That species is always destitute of avicularia ; 

 whilst in S. marmorea there is usually one below the 

 orifice, occupying much the same position as in 8. reticu- 

 lata. There are also diflFerences in the denticle on the 

 lower margin, which in the present species assumes the form 

 of a very broad plate. 8. marmorea, so far as I know, is 

 destitute of the deep-red colour which is so characteristic 

 of its allv. 



Apart from these divergences, which in the aggregate 

 are not unimportant, there is a difference in general ap- 

 pearance which can hardly be formulated. 



I have only seen a few specimens of 8. marmorea ; and 

 possibly a larger series might show an intermingling of 

 characters ; but at present I hold the two forms to be 

 distinct. 



SmITTIA BELLA, Busk. 



Plate XLII. figs. 9, 10. 



Lepralia BEIJ.A, Bxisk, Quart. Journ. Micr. Sc. viii. (1860), 144, pi. xxvii. 

 fig. 2 (not L. bella, Norman, Shetland Polyz., Kep. Brit. 

 Assoc. 1868, 306, which is avar. ot Porella concinna). 



Zooecia ovate, punctured ; aperture orbicular, with a spout- 

 like sinus below, and within it a large bifid denticle ; 

 peristome raised, often thickened. Ooecia subglobose, 

 punctured. 



Habitat. On shells. 



Locality. Shetland (Barlee). 



