LAMELLIBRANCHIA TA . 
441 
The suggestion of the variety occidentalis came from specimens occurring in 
western localities, preserving the shell with all its exterior markings, in which 
condition it has not been found in the Corniferous limestones of New York nor 
in Ohio, so far as observed. A comparison of a large number of specimens, in 
all conditions of preservation, indicates no differences of.character which are of 
varietal importance. 
Formations and localities. In the Corniferous limestone of Western New York, 
Canada West, Michigan and Ohio; also in the limestone of the age of the 
Hamilton group at the falls of the Ohio, and Clarke county, Ind. 
Paracyclas lirata. 
PLATE LXXII, FIGS. 2-19 ; AND PLATE XCV, FIG. 19. 
Posidonia lirata, Conrad. Geol. Surv. N. Y., Ann. Rep., p. 116, pi. [no number], fig. 12. 1838. 
Lucina (Paracyclas) lirata (Conrad), Hall and Whitfield. Twenty-fourth Ann. Rep. N. Y. State Mus. 
Nat. Hist., p. 200. 1872. 
In part Paracyclas lirata (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates arid Explanations: PL 72, 
figs. 1-19. 1883. 
Shell of medium size, sub-circular or broadly elliptical; length a little greater 
than the height; margins regularly rounded. Cardinal line short, less than 
half the length of the shell. 
Valves moderately convex below, becoming gibbous on the middle and 
above. 
Beaks anterior to the centre, small, appressed, rising but little above the 
hinge-line. Post-cardinal slope not defined. 
Surface marked by fine concentric striae, and by strong sub-angular con¬ 
centric ridges, which are more or less sharply defined, depending upon the 
condition of the specimen and the nature of the matrix in which the fossil is 
imbedded. 
Ligamental grooves distinctly marked and only moderately divergent from 
the cardinal margin. 
Four specimens measure respectively 15, 19, 25 and 28 mm. in length, and 
13, 18, 22 and 25.5 in height. 
