NIAGARA SROXTP. 



171 



appears to be oval, and surrounded by a thin calicle. Where worn down, the form of the 

 aperture changes, and is more or less tripetalous or irregular. Under an ordinary magnifier the 

 cells appear like minute papillose points, with an oval or roundish aperture, and the variety of 

 form is scarcely perceptible. 



Fig. 4 a. A fragment of a larger frond. 



Fig. 4 i. A portion of the surface enlarged, shelving the papillose cells, and tubercles with 



smooth summits. 

 Fig. 4 c. A small portion still further enlarged, showing some variety in the form of the apertures. 



Position and locality. In the shale of the Niagara group at Lockport. 



Genus LI CHEN ALIA ( nou. gen. ). 

 [Gr. Ai;;,^svfj£, liche//, and a'Kws, marine.] 



Membranous or subcalcareous bryozoa, growing in circular or flabellate forms, concentrically 

 or radiately striate, ceUuliferous on one surface only ; frond usually a thin membrane, though 

 often unequally thickened and contorted or wrinkled. 



This genus includes several species of Bryozoa, which usually occur in circular or expanded 

 forms presenting a striated surface. It is only in raie instances that distinct cells are visible, 

 though in most cases the surface appears marked as if by stigmata, or the commencement of 

 cells, which sometimes rise in low nodes without presenting any defined apertures. Although 

 many specimens have been examined, it is still diflicult to point out the true relations of these 

 forms. The genus is perhaps more nearly like Diastopora or Udotea than any others, but 

 it possesses characters entirely peculiar, and is probably a true palaeozoic type. 



567. 1. LICHENALIA CONCENTRICA (n. .sy>.). 



Pl. XL E. Fig. 6a-g. 



Frond circular, slightly cup-form in the young state, flattened at maturity, and often variously 

 contorted from irregular growth or accident, and thickened at intervals ; surface concentrically 

 marked by fine striae and prominent concentric folds or ridges ; ceUuliferous side less strongly 

 striated, cells arranged in concentric lines, almost coincident with the strife ; apertures of cells 

 narrow, opening upon the summit of an elevated pustule ; non-celluliferous side of the frond 

 showing oval stigmata, produced by the bases of cells on the opposite side. 



This fossil, in its young state, is often found in a tolerably perfect condition ; but in more 

 advanced stages, as the size increases, its fragile structure has suffered injury and distortion in 

 various ways. The young specimens differ little from the membranous envelope of the base of 

 a Ch^tetes or Favosites, but they are never found with the structure of these genera. The 

 older and larger specimens are usually broken, and in some instances they are folded together 



