LAMELLIBRANCHIA TA. 
515 
MEGAMBONIA, Hall. 1859. 
Megambonia cardiiformis. 
PLATE LII, FIGS. 1-8. 
Pterinea cardiiformis, Hall. Geol. Rep. Fourth Dist. N. Y., p. 172, fig. 1. 1843. 
Megambonia cardiiforvm, Hall. Twelfth Ann. Rep. N. Y. State Cab. Nat. Hist., p. 13. 1859. 
“ “ “ Pal. N. Y., vol. iii, p. 272. 1859. 
“ subcardiforniis, “ S. A. Miller.* Cat. Am. Pal. Foss., p. 194. 1877. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations :* PI. 52, figs. 1-8. 1883 
Shell large, cardiiform, higher than long; basal margin regularly rounded; 
posterior margin curving abruptly upward to the cardinal line; cardinal 
margin sub-alate posteriorly. Anterior end short, auriculate, separated from 
the body of the shell by a distinct byssal sinus, which is conspicuously 
marked in the margin of the shell. 
Valves regularly convex, very gibbous in the umbonal region; the depth 
of the two valves is somewhat less than the length of the shell. 
Beaks sub-anterior, incurved; umbo prominent, rising above the hinge-line. 
Test thick, marked by concentric lamellae of growth and by fine radiating 
striae. 
Anterior muscular impression large and deep, situated within the auricle 
and occupying a large part of the lobe. Posterior muscular impression large, 
situated near the post-cardinal extremity. There is an obscure indication 
of a lateral tooth on the post-cardinal angle. 
A large and nearly perfect specimen has a length of 59 mm. and a height 
of 73 mm., with a depth to both valves of 46 mm. A larger specimen has 
a height of 76 mm. and a transverse diameter of 64 mm. 
This species somewhat resembles M. bellistriata of the Oriskany sandstone, 
but differs in its greater gibbosity, shorter and more oblique sinus, separating 
the auricle. 
Formation and locality. In the upper member of the Corniferous limestone 
at Clarence Hollow, Erie county, N. Y. 
* The reference of this species under the specific name of subcar diformis has come jCrom copying- an 
erroneous manuscript record of the species. 
