280 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



ORTHIS (FINKELNBURGIA) OSCEOLA CORRUGATA, new variety. 



At two localities of <A (I'Z) osceola a few specimens occur which 

 have strong concentric ridg-es formed by the piling up of lines of 

 growth. The shell has a corrugated appearance that is very distinc- 

 tive and it is designated as a variety. 



Formation and locality. — Upper Cambrian. St. Croix sandstone, 

 Osceola Mills, Wisconsin. Just below DiceUocej^halus minnesotensis 

 beds, Winona, Minnesota. 



PROTORTHIS Hall and Clarke. 



Protorthis Hall and Clarke, Pal. N. Y., VIII, 1892, Pt. 1, p. 231, pi. vii a, 

 figs. 14-21; Eleventh Ann. Rep. State Geologist New York, p. 273, pi. viii, 

 figs. 3-7. 



Billmgsella Schuchert, Bull. U. S. Geol. Sur. No. 87, 1897, p. 334. 



Original diagnosis. — Shells small, transversely subquadrate or semicircular. Hinge- 

 line straight, its length being equal to the greatest width of the valves. Valves 

 unequally biconvex, or subplanoconvex, the pedicle-valve being the larger. The 

 cardinal area is narrow on both valves, but is higher on the [ventral] pedicle- valve, 

 and is transected by a broad delthyrium, which is closed below by a concave plate 

 apparently produced by the union of the dental lamelUe, which are not continued to 

 the bottom of the valve; teeth distinctly developed. In the [dorsal] brachial valve 

 the cardinal area also bears an open delthyrium; the dental sockets are obscure and 

 the crural plates small; the latter appear to unite and forma low elevation across 

 the base of the delthyrium. Cardinal process absent or rudimentary in all the speci- 

 mens examined. Muscular markings in both valves extremely obscure. 



Surface marked by distinct plications, with interstitial finer radii, which are crossed 

 by delicate concentric strife; these are usually accompanied by a low sinus and fold 

 on the brachial and pedicle-valves, respectively; interior very finely papillose. 

 Shell-substance fibrous and apparently punctate. 



Type. — Ofthis Billingsi Hartt. St. John group. 



The characters of the St. John species are eminently comprehensive; first, the 

 form of the shell is one more frequently met with among the strophomenids 

 than among the orthids; the concave plate formed by the union of the dental 

 lamellae is never found in Orthis proper, though occurring in Scenidium. In Orthisina 

 or (Mtamhonites this plate is always present, but always supported by a median 

 septum and invarial)ly accompanied by the convex deltidium, which, so far as 

 known, does not exist in Protortlils; while in the group typified by (frthis Pepina, 

 Hall (here designated by the term BiUingseUa), the convex deltidium of Clitam- 

 honites is present and the concave or dental ]>late absent. The apparent absence of 

 a cardinal process in Protorthis may be due to tbe imperfections of tlie fragile shells 

 studied. The specimens of the St. John shells are preserved as external and inter- 

 nal casts, and from some of these there is reason to infer that the substance of the 

 shell was punctate. 



Ohservatio7i.s. — A study of the various species here described under 

 the genus Protorthis. has not given data that will add to the above 

 generic description. All of the species have evidence of punctfe of 

 greater or less depth on the inner and outer surfaces of the shell, but 

 in none of them have punctse been found that penetrated through the 

 shell; this ma}" be owing to the fact that all of the species are pre- 



