MEMBRANIPORELLA MELOLONTHA. 203 



Zocecia ovate, produced below, distant, separated by a 

 deep and wide groove, disposed in linear series ; the 

 central portion of the fi'ont wall composed of about eight 

 flat ribs, closely contiguous, on each side, forming an 

 oval figure, which is surrounded by a border of smooth 

 cell- wall ; mouth semicircular, a stout tubular process 

 on each side, projecting like a tusk, and two slender 

 spines above (often wanting) ; at the lower end of the 

 cell, immediately under the ribbed portion, a conical 

 process, inclined upwards. Avicularia none. Ocecia 

 unknown. 



Primary cell small^ suborbicular, raised; surface smooth, 

 solid ; area occupying the whole upper part of the cell, 

 with membranous covering ; no spines. Two normal 

 cells originate from the primary zooecium ; and as growth 

 proceeds the successive series widen, so as to produce a 

 somewhat fan-shaped figure. 



Colonies spreading in dendritic fashion, with a tendency 

 to rise into delicate free expansions. 



Range of Variation. There is very little variability in 

 this species as compared with the last. The number of 

 ribs is pretty constant (six to eight) . When young and 

 fresh, the cells are hyaline and glistening ; they become 

 dense and opaque with age. 



Habitat. On shells, especially on the oyster, at the 

 mouths of rivers. 



Localities. Estuary of the Thames (Lieut. Thomas) : 

 near the mouth of the Orwell, coast of Suffolk (Busk) : 

 East coast (Mrs. Gatty) : Roach River (Mr. Jeffi'eys)*. 



* If Mrs. Gattj was right in identifying Dr. Johnston's dendritic variety 

 of Lepralia niticla with the present species (and it is probable that she was), 

 Kirkwall Bay must be added to the list of localities, on the authority of 

 Lieut. Thomas. 



