231 LiGNiTic Stage 39 



lateral areas, an elliptical-circular muscular scar situated very 

 near the center of the valve, a slight dehiscence anteriorly, and a 

 stronger one posteriorly, and profound depression central-pos- 

 teriorly for the soft parts; right valve operculate, somewhat sin- 

 uate anteriorly and posteriorly to partially or wholly counteracft 

 the gaping tendency of the left valve; ligamental pit not deep, 

 but well defined, with moderate lateral areas; muscular impression 

 elliptical-circular; greatest thickness just within the periphery. 



This form has for some time been a source of annoyance to the 

 writer, for it certainly has characflers in common with O. com- 

 pressirostra, O. carolinensis , O. trigonalis, and O. sellceformis. 

 It is from the Lignitic horizon, hence in O. compressirostra one 

 would expect its closest ally. It differs, however, from O. com- 

 pressirostra by its circular-quadrate form, incrassated valves, cir- 

 cular muscular impression, paucity of ribs in adult form, and 

 entire want of the same during earlier stages of growth. 



This species is doubtless the one referred to hy Tuomey in his 

 ist Biennial Report, p. 146, for he says the shells are large and 

 ponderous and resemble very closely a variety of O. compress- 

 irostra found on Santee canal, South Carolina. This statement 

 evidently led Conrad to supppose, Amer. Jour. Sci., 2d ser. , vol. 

 40, p. 266, 1865, that this oyster was really O. carolinensis de- 

 scribed by himself in 1832, Foss. Shells, Tert. Form, p. 27, pi. 

 14, and he makes this amendment in Tuomey's list. Heilprin, 

 however, states that in the copy of Tuomey's report in the Phila- 

 delphia Academy the following is written in pencil a propos of 

 Tuomey's list : " All doubtful except Venericardia planicosta. T. 

 A.Conrad." Heilprin does not specifically identifj^ the oysters 

 contained in the collections he studied and reported upon from 

 Knight's and Cave Branches and Woods Bluff for Dr. E. A. 

 Smith, Proc. Acad. Nat. Sci., 1880 pp. 364-366; nor does Aid- 

 rich give specific names to these forms in Bulletin No. i of the 

 Alabama Survey, 1886. The young form here shown pi. 6, figs. 

 3, 4, he doubtless refers to as "Ostrea (probably O. thirscey 



Smith and Johnson, however, in Bull. 43, U. S. Geol.Surv., p. 

 44, 1887, designate this oyster as "O. compressirostra Say, with 

 very thick and ponderous shells. ' ' 



True it is we may yet doubt whether the numerous thin young 

 oysters, found for example, in the upper part of the Woods bluff 

 outcrop, are the representatives of the full grown specimens in 

 the concretionary layers below. Yet we have seen an approach to 



