376 
THE PALEONTOLOGY OF MINNESOTA. 
[Pholidops. 
Genus PHOLIDOPS, Hall. 
1859. Pholidops, Hall. Palaeontology of New York, vol. iii, pp. 489, 490. 
1892. Pholidops, Hall. Ibidem, vol. viii, pt. i, p. 155. 
Description: "Shells small, patelliform, equi valve, equiconvex, inarticulate, 
unattached. Outline oval or subelliptical; apex subcentral, excentric or marginal, 
sometimes terminal and produced. Surface marked by strong, concentric, often 
lamellose lines of growth, v^hich are crowded on the posterior and distant on the 
anterior portion of the valves; these are sometimes crossed by faint, interrupted 
radiating lines. In the interior the surfaces of contact make a broad, smooth, flat 
or slightly convex border, somewhat broader in front than behind. The muscular 
and visceral area occupies a sharply-defined and very limited space in the apical 
portion of each valve. In both it is of essentially the same size and subtriangular 
in outline, the apex of the triangle pointing forward and usually surrounded by a 
conspicuous callosity. 
"The ventral(?) valve bears two well-defined central adductors occupying the 
same relative position as in Crania; these impressions are usually simple, but appear 
to be sometimes complicated by association with ill-defined scars of the anterior 
muscles. The posterior adductors or divaricators are situated at the basal angles 
of the muscular triangle and are distant from the posterior margin. The linear 
parietal scars are very strong, the posterior being more or less distinctly lobate, the 
anterior generally straight or rounding about the central adductors. In the opposite 
or dorsaU?) valve the scars have essentially the same arrangement; the anterior 
adductors, however, are separated by elongate median scars (anteriors) which traverse 
the elevated callosity surrounding the anterior margin of the area. The posterior 
scars are often more widely divergent than in the other valve. Shell substance cal- 
careous and impunctate(?)." (Hall, 1892, op. cit.) 
Type: Orhiciila ? squamiformis Hall. 
Pholidops trentonensis Hall, var. minor, n. rar. 
plate XXIX, FIG. 40. 
The original description of P. irefitonensis Hall* is as follows: "Shell small, 
broadly oval, very depressed-convex. Apex situated near the cardinal extremity. 
Surface marked by strong, concentric, lamellose lines of growth.'' 
The Minnesota specimens in outline, convexity of valves, position of the apex 
and the strong lamellose lines of growth, agree with these parts as described and 
illustrated in P. trentonensis Hall. They are, however, one-half, but more often less 
* Descript. of new species of Crinoidea and other Fossils, p. 14, 186C. Twenty-fourth Rep. N. V. State Cab. Nat. Hist, 
p. 221, pi. VII. fig. 8, 1872. 
