15 St. Maurice and Ci.aiborne Pelecypoda 15 



Gabb had before him in naming mortoni, is quite sufficient to 

 prove their identitj^ with vicksburgensis. One specimen, Morton's 

 original of fig. 10 and used by Gabb as one of his mortoni, had a 

 general resemblance to our form hidovidana. The radiating ridges 

 are rather sharp plications than rounded ribs so common in hido- 

 vidana — somewhat like the ornamentation of the Miocene sicbfal- 

 cata. It passes insensibl}' into coarsely plicate vicksbiirgensis two 

 or three inches in diameter. 



Varietal diaraderization . — General form and size as figured ; 

 left valve gibbous, extended at lower posterior margin ; ribs on 

 post-umbonal slope faint, generally about six in number ; anter- 

 iorly, ribs strong, 6-12 often bifurcating, especially strong from 

 beak to posterior margin. Lesser valves concave, decided!}- of 

 the appearance of the lesser valves of some small Exogj'-ras. 



Type. — Harris collection at Cornell Univ. No's. 2-6, Natch- 

 itoches, La. ; I, 7-10, Chestnut, La. 



Geologic horizon. — St. Maurice Eocene. 



Localities. — Especially in Natchitoches Parish, La., about 

 Natchitoches, Provencal, Robeline and Chestnut ; also Bienville 

 Parish and Columbus, Sabine Parish. That it occurs as far east 

 as Alabama several not exactly localized specimens from this 

 State in the Museum attest. Long drawn out, claw-shaped mu- 

 tations are common along the Sabine River, near Columbus. 



Ostrea johnsoni, PI. 10, figs. 11-15. 



0.johnso)ii Aid., Bull, i, Ala. Geol. Surv., 1886, p. 41, pi. 6, fig. 6. 



Aldrick's original description. — "Shell large, thick ; both valves con- 

 vex ; beaks pointed in lower valve ; breadth of shell greater than length ; 

 both valves strongly plicate, generally with six folds, the plications becom- 

 ing very deep with age, the concave part between the two basal folds run- 

 ning out into a long curved tongue ; surface strongly laminated, laminae 

 terminating at edge of shell ; attachment scar not visible ; ligamental area 

 with a rather deep, transversely striated furrow in the lower valve, shallow- 

 er and broad in the upper ; muscular scar, large nearest the base and pos- 

 terior margin ; curved, spatulate, nearly straight on iipper side. 



This form seems to be confined to the Lower Claibornian above the 

 Buhrstone." 



Dali remarks (Trans. Wag. III. p. 681) : "This is an excellent 

 species with a few strong plications, making the valves claw-like." 



