188 TRANS. OF THE ACAD. OF SCIENCE. 
~eewyptil sees sharp, terminal, curved in and forward. The sur- 
Jace arked with numerous imbricating lines of growth, 
er. 
gr eight from the beak to the basal extremity, 1.96; width 
from the anterior to va posterior margins, .86; thickness, a 
Our shell m the I. rectus, Shamard, i in havi 
concave anterior siisath ; beaks curved forward, posterior wal 
gin parallel with the anterior, and a more abrupt oe 
angle between the cardinal and posterior margins. 
tus, Goldfuss, (Pet. P- 169, pl. 128, fig. 7,). from the Muschel 
kalk, is less _—— n the anterior margin, not Ue thick and 
the extremity of ny em not so near the anterior margin. 
Maj. Hawn’s ream from the Permian(?) strata in K. > 
| Mrrrvs aeredinal) concavus, Swallow. 
Shell short, triangular, marked with sub-imbricating lamine 
or lines of growth, which are concentric on the posterior car- 
dinal slopes, b y diver ging on the concave 
anterior surface. Anterior margin concave, nearly as long a8 
the shell; cardinal margin long, straight or slightly convex} 
_ posterior basal m margin regular! ly curve ed from the cardinal to 
the anterior margin, with both of which it forms angalar jus 
tions ; anterior slopes so flattened as to present a sharply de s 
ow, even, concave ag as long as the anterior margiD, and 
the thickness Dg inal Marge Her eer: 
