12-1 PROCEEDINGS OF THE ACADEMY OF 



unite" Cryptonella and Centronella "until a reexamination of the original 

 specimens of Mr. Billings shall confirm his first observations, or show them to 

 correspond with" Cryptonella. It is this hesitation to admit the inevitable 

 consequence, and to retract his honorable and friendly, but unfounded criti- 

 cism, which induces me to reassert the correctness of my generic reference of 

 Centronella Julia, resting as it does upon the original description and figure, 

 and the observed characters of the type of the genus, as well as the subsequent 

 confirmation of the author of the genus, himself. 



OSTREA, Linmuus. 



Ostkea rATERCCLA, n. sp. Shell adherent, thin, small, ovate, deeply boat- 

 shaped, with the deeply excavated beak of the lower valve prominent, incur- 

 ved and somewhat posterior. The muscular scar is large, transversely broad- 

 reniform, concave on the cardinal side, situated nearly midway between the 

 centre of the valve and its posterior margin, and is marked by two transverse 

 lamellose lines. The deepest part of the valve is midway between the centre 

 and the beak ; the depth is nearly the same for as great a distance on the 

 other side of the centre. The exterior of the shell is irregular with concen- 

 tric lamellose lines of growth. 



Greatest length, "65 (100) ; greatest width, *40 (61) ; greatest depth of 

 lower valve, '25 (35) ; depth of cavity of the beak, *15 (23). 



From the buff sandstone at the base of the Burlington limestone, Burling- 

 ton, Iowa. " White Collection " of the University of Michigan. 



The unexpected discovery of this oyster believed to be the most ancient at 

 present known together with its somewhat cretaceous aspect, awakened a 

 suspicion that it had not been found in place. To certify myself on this point, 

 I addressed Dr. White on the subject, and received the following reply : "The 

 Ostrea, if I remember rightly, was imbedded in a white or light gray, silicious 

 material, of chalky appearance, containing some remains of dririoids and shells. 

 My impression is, also, that it was from a quarry about half a mile north of 

 my residence, and in the lower bed of the Burlington limestone, and not far 

 from its base. I think the label which accompanied it, and also my letter at 

 the time, may be entirely relied on. I admit the possibility of error, but I do 

 not believe there is any." 



Ptebinea ceenistbiata, Win. (Carcliopsis crenistriata, Win., Proc. Acad. 

 Nat. Sci. Phil. Sept. 1862, p. 417.) More perfect specimens from the typical 

 locality of C. crenistriata reveal the fact that the species is possessed of an an- 

 terior wing, which is a mere flattened portion of the anterior angle of the car- 

 dinal line, with a barely perceptible sinus beneath. This feature does not 

 belong to Carcliopsis as defined, and establishes a probable conformity with 

 Pterinea. 



The right valves recently discovered might be mistaken for another spe- 

 cies. They show no radiating lines, except near the hinge, behind the beak. 

 The concentric markings are only small, irregular wrinkles of growth, with 

 none of the sharply raised lines which characterize the other valve. It is of 

 course possible that these right valves belong to another species, but as they 

 have exactly the form of the crenistriated valves, and the latter are all left 

 valves, it seems probable that they belong together. 



Ptekinea spinalata, n. sp. (Avicula acanthoptera t Win., Proc. Acad. Nat. 

 Sci. Jan. 1863, p. 8 ; not A. acanthoptera, Hall, Geol. Rep. 10th Dist. N. Y. p. 

 263.) Careful comparison with the types of A. acanthoptera, Hall, convinces 

 me that the Iowa specimens ought to be separated. The left valve of A. acan- 

 thoptera, Hall, has the body of the shell broader than in the Iowa specimens, 

 and. both wings are less defined. The right valves, also, are much Hatter. 



Amongst the Iowa specimens appear to be two types one with the body of 

 the valve arcuate, and the other with it straight. The former type was 



[July, 



