VINE : NOTES ON YORKDALE TOLYZOA. 
87 
regular distances, in tlie other case (Scotch) wide apart and thin. 
The ZoiBcia in the American examples, are seven to a line in length, 
and in this respect the Scotch examples differ very much, for they 
are at most either six or five-and-half to the same space, but in the 
American species there is a tubercle to nearly every cell in the 
central portion of the branch, seven to a line, while in the Scotch 
form, there are often only three or at most five to a line. In the 
American form, the waving striee between the cells are not a marked 
feature, whereas even in partially preserved Scotch examples this 
feature is very striking-. I cannot make much of the angularity or 
rotundity of the reverse aspect of tlie American and Scotch forms, 
because these features vary greatly, and above all both Mr. J. M. 
Nickles, and I believe Mr. Ulrich also, deny the affinity of the Scotch 
and American Folypora tuherculata, and I believe rightly so. Before 
describing the Yoredale forms I felt that it was incumbent on me to 
direct attention to these special features, because both the Lancashii e 
and North Yorkshire forms are related to the Scotch but not to the 
American species. With regard to the tuberculation of the surface, 
P. biarnarca Keys, is likewise tuberculate, and even the name M'Coy 
selected for his species, verrucosa, would suggest a similar feature, 
even though he might not characterise it. The following is a full 
description of Front's species diagnosed from American examples : — 
PoLYPORA TUBERCULATA, Prout, Tran. Acad. Soc, St. Louis. 
(See note J. Young, Geol. Mag,, 1874, p. 258). 
Zoarium a fan-like expansion. Branches (average size) -^V of 
an inch in breadth, pretty uniform in size, suddenly enlarging before 
and after bifurcation, dichotomising opposite on two branches, at one, 
one-and-half, and nearly two lines apart. Dissepiments about one 
third as large as the branches, occasionally expanding at their 
junction with the branches. Fenestrules oblong, subquadrangular, 
sometimes shortly spatulate or irregular near the bifurcations. 
Zomcia small round, eleven to twelve cells to three millemetres, 
penistomes thin, circular, and very slightly raised, tubercles small, 
one to every cell, on the central part of the branches, occasionally 
absent from the marginal cell, but not invariably so ; some of the 
tubercles overhang the orifice of the cell like the ovicell in the 
