126 PROCEEDINGS OF THE ACADEMY OF 



Avicula laevigata, de Koninck, from the carboniferous limestone of Belgium, 

 &c. &c. 



This genus is known to have existed in the Chemung of Phillipsburg, New 

 York,* whence it probably continued to the epoch of the Burlington lime- 

 stone. An uudescribed species occurs iu the fine grained sandstone of Ohio. 



Pernopecten lim^formis, Winchell. {Aviculopecten limceformis, White and 

 Whitfield.) In this typical species, the number of ligamentary pits is about 

 seven on each side of the mesial one. The hinge line is short, and the auri- 

 culations are small and Lima- like. 



Pernopecten limatus, n. sp. Shell rather small, moderately ventricose, 

 subcircular. Body of shell bounded by two straight lines diverging from the 

 beak at an angle of 126, and proceeding to the superior lateral margins, from 

 which points the outline of the .^hell is very nearly circular. Hinge line 

 straight, a little more than one-third the greatest width of the shell ; ears 

 very small, flattened, subequal ; the anterior (of the left valve) making an 

 angle of about 10(5* with the hinge line, and 120 with the body of the valve ; 

 the posterior ear forming an angle of 129^ with the hinge line and 146 with 

 the body of the shell. Beak small, inconspicuous, not projecting beyond the 

 hinge line. Convexity of the valve nearly a segment of a sphere, a little more 

 elevated in the umbonal region. Surface extremely smooth. 



Dimensions parallel with the hinge 1*20; at right angles with the hinge 

 1*05 ; length of hinge line *40 ; length of anterior slope of body of valve - 59 ; 

 of posterior slope - 47 ; convexity of left valve '17. 



From the base of the Burlington limestone, Burlington, Iowa, a horizon 

 identified by its fauna with the yellow sandstones below, (compare my paper, 

 Proc. Acad. Nat. Sci. Phila., Jan., 1863, p. 25). "White Collection " of the 

 University of Michigan. 



* The internal hinge structure of this species has not been observed, but the 

 auriuulations are scarcely such as belong to Aviculopecten, as defined by 

 McCoy, while they present a close conformity with the foregoing species. 



Aviculopecten occidental it, Win., differs from this in its longer cardinal 

 slopes, making a smaller angle with each other, and in its longer hinge line, 

 with larger and distinctly ribbed auriculations. 



Pernopecten Shumardanus, Winchell, {Avicula circulus, Hall, not Shu- 

 mard). It is scarcely possible that the species identified by Hall (Iowa Rep. 

 022, pi. vii. fig. 9) as A. circulus, Shum., (Missouri Rep. 206, pi. c. fig. 14), 

 can be the same species. Prof. Hall's figure and description do not show it ; 

 nor do specimens from the same bed, commonly regarded as A. circulus, Hall, 

 present satisfactory correspondence. The shell has a much shorter hinge 

 line, with smaller ears, joining the cardinal slopes by obtuse angles. More- 

 over the concentric lines are very regular, and the radial ones are faint, irre- 

 gular dashes, entirely unlike the continuous and distinct though diminutive 

 ribs of A. circulus, Shumard. 



Yielding to the suggestion of Dr. White, I formerly identified A. circulus, 

 Hall -before I had seen actual specimens with Aviculopecten limceformis, 

 White and Whitfield. I am convinced, however, on careful comparison of 

 specimens, that we must regard A. circulus, Hall, as a distinct species. 



In general characters this species resembles P. limatus, and only differs in 

 its shorter and less sharply defined cardinal slopes, and the presence of the 

 two systems of superficial markings. 



PINNA, Linnaeus. 



Pinna ? Marshallensis, n. sp. Shell small, equivalve, compressed, lance- 

 olate, squarely truncate and gaping at the extremity opposite the hinge, and 



* I find tbat Prof. Hall has also marked this form as a distinct frenus. 



[July, 



