126 
PROCEEDINGS OP 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 undescribed species occurs, in 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- 
eulations 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 shell 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 106° with the hinge line, and 120° with the body of the valve ; 
the posterior ear forming an angle of 129 w 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. Pliila., Jan., 1863, p. 25). “White Collection ” of the 
University of Michigan. 
The internal hinge structure of this species has not been observed, but the 
auriculations are scarcely such as belong to Aviculopecten, as defined by 
McCoy, while they present a close conformity with the foregoing species. 
Aviculopecten occidentals, 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 Pep. 
522, 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 an(i|Whitfield. I am convinced, however, on careful comparison of 
specimens, mat 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 that Prof. Hall has also marked this form as a distinct genus. 
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