Lamellibranchiata. 331 



GLYPTODESMA, Hall. 

 Glyptodesma erectum. 



Avicula erecta, Conrad. Jour. Acad. Nat. Sci., Phila., p. 328, pi. 12, fig. 5. 



1842. 

 Avicula cruciformis, Conrad. Geolog. Surv. N. Y. : Ann. Rep., p. 54. 1841. 

 Actinode&ma erectum (Conrad), Hall. MS., Pal. N. Y. 1877. 



S. A. Miller. Cat. Amer. Pal. Fobs. 1877. 

 erueiforme (Conrad), Hall. MS., Pal. N. Y. 1877. 



" S.A.Miller. Cat. Amer. Pal. Foss. 1877. 

 Glyptodesma erectum (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and 

 Explanations: PL 11, figs. 1-10; pi. 12, figs. 1-3. 5-9; pi. 13, figs. 1-4, 

 12-15 ; pi. 25, figs. 14-17. Jan., 1883. 



Shell large ; body ovate, acute, erect or moderately oblique ; wings 

 more or less expanded, often greatly expanded; height frequently 

 one-third greater than the length ; basal margin more or less regu- 

 larly rounded ; anterior side broadly convex ; posterior side nearly 

 straight or slightly concave. Valves very unequal. Left valve vary- 

 ing from moderately convex to gibbous and arcuate. Right valve 

 depressed-convex in the umbonal region, flat or concave below ; 

 variable in convexity. Hinge-line straight, often greatly extended, 

 equaling or usually greater than the length of the valve. Beak of 

 left valve prominent, acute, inclined forward, rising above the hinge- 

 line, and situated anterior to the middle of the body of the shell. 

 Umbonal region somewhat prominent, often gibbous, limited an- 

 teriorly by a distinct rounded sulcus, and posteriorly by an inter- 

 ruption and change in the direction of the striae, which sometimes 

 produces a defined line of separation. UmbonaUangle acute. An- 

 terior wing auriform and small in young specimens, becoming ex- 

 panded and variously extended in older specimens, limited by a dis- 

 tinct byssal depression ; extremity rounded. Posterior wing large, 

 triangular ; margin concave ; extremity often extended beyond the 

 margin of the shell. 



Test thick, marked by fine, irregular, concentric striae of growth 

 which are sometimes raised into sharp lamellae, or crowded into 

 prominent fascicles. These striae become more conspicuous upon 

 the margins and upon the wings, where they are often highly lamel- 

 lose. The distant lamellae which mark the body of the shell are 

 sometimes continued upon the hinge, and becoming stronger, curve 

 over the margin, giving it a sharply annulated aspect, which, when 

 preserved in the impression of the hinge-border, might be mistaken 



