SILURIAN llADIATA. 173 



the smaller size of the cell-tubes and their greater number in 

 a given space, their proportionate distance being pretty nearly 

 the same. In both the British and foreign specimens the cells 

 are so beautifully distinct, that it would be impossible to over- 

 look the notches or rudimentary lamellae if they existed. 



Forming large masses not uncommonly in the Wenlock lime- 

 stone near Aymestry. 



[CoL University of Cambridge.) 



POLYZOA. 



Berenicea heterogyra (M^Coy). 



Sp. Char. Parasitic, often on Ortkoceratites, covering spaces of 

 upwards of 2 inches square; cells disposed in irregular radiating, 

 or divaricating, circular, or fan-shaped lines, ten or eleven oc- 

 cupying the space of 1 line (measured across their length), and 

 about three in the same space in the direction of their length, 

 each cell slightly more than the third of a line long, very nar- 

 row, fusiform, about four times longer than wide, and sepa- 

 rated by a space, varying from their greatest width to less than 

 one half their width or nearly in contact ; upper convex sur- 

 face of each cell with four or five large tubercles when well 

 preserved. 



The cells of this remarkable species are almost invisible to the 

 naked eye, but it occurs forming patches of considerable size ; 

 the small size of the cells and their very elongate slender form 

 distinguish this species from the B. irregularis of Lonsdale. 



Coniston limestone of Coniston. 



{CoL University of Cambridge.) 



Ptilodictya explanata (M^Coy). 



Sp. Char. Corallum forming large funnel-shaped foliaceous 

 flexible expansions upwards of 2 inches wide ; axis semimem- 

 branous, very thin, marked with small, close, concentric or 

 forward- curved undulating wrinkles; tube-cells pyriform ob- 

 lique, three or four times longer than wide, narrowed poste- 

 riorly, anterior ends of the adjacent cells convex rhomboidal, 

 with a round perforation nearest the anterior edge; cells 

 separated by depressed lines, which (when finely preserved) 

 show one or two alternating rows of small cellules, about 

 seven or eight cells in a space of 2 lines. 



The broad foliaceous expansions of this species readily distin- 

 guish it from any of those described by Mr. Hall, as well as the 

 very narrow depressed spaces between the cells on the surface, 

 and the broad rhomboidal, convex portion of the cells surround- 

 ing the aperture. Finely preserved casts of the surface show 



