MICROPORELLA VIOLACEA. 219 



Var. ft (plagiopord). West off Tortugas, in 60 fathoms 

 (Pourtales) : France, S.W. (Fischer). 



RANGE IN TIME. Italian Pliocene deposits, very abun- 

 dant, forming very large colonies of a dark-grey colour 

 (Manzoni) : Tertiary beds at Sollingen (Reuss) : Coralline 

 Crag (S. Wood) : Middle Pliocene ( = Coralline Crag and 

 Red Crag, part) (A. Bell) . 



In the oldest and most worn condition this species may 

 be recognized by the central depression and pore, and the 

 foramen which marks the position of the avicularium. 



The Tertiary L. diversipora of Reuss is, I think, referable 

 to M. violacea, the only point in which it seems to differ 

 from the recent form being the shape of the central pore, 

 which is described as crescentic. In fossil specimens the 

 double pore of the var. a might probably be represented by 

 such a figure ; but in any case so slight a difference could 

 hardly of itself be accounted distinctive. 



A curious point in the history of M. violacea remains 

 to be noticed. Scattered over the colony, usually in 

 small groups, cells of abnormal size are often to be met 

 with, which are furnished with a narrow slit-like mouth, 

 much extended transversely, and filled in by a corneous 

 operculum. These gigantic cells are about twice the size 

 of the ordinary zooecia. They are ovate in F . 1% > 

 form, and want the central depression ; the 

 pore, however, occupies its usual position ; 

 and the avicularium is present, though re- 

 duced in size and separated by a space from 

 the orifice. They are probably cells modi- 

 fied for the discharge of reproductive func- 

 tions. M. violacea is one of the species on 

 which ovicells have not been noticed. Young cell. 



