LA MELLIBRAN CHI A TA. 
153 
GLYPTODESMA, Hall. 
Glyptodesma erectum. 
PLATE XI, PIGS. 1-10; PLATE XII, PIGS. 1-3, 5-9; PLATE XIII, PIGS. 1-4, 12-15; PLATE XXV, FIGS. 14-17; 
PLATE LXXXVI, FIGS. 1-8; and PLATE LXXXVII, FIGS. 1-3. 
Avicula erecta, Conrad. Jour. Acad. Nat. Sci., Phila., p. 238, pi. 12, fig-. 5. 1842. 
“ cruciformis, Conrad. Geolog. Surv, N. Y.: Annual Report, p. 54. 1841. 
Actinodesma erectum (Conrad), Hall. MS., Pal. N. Y. 1877. 
“ “ “ S. A. Miller, in Cat. Amer. Pal. Foss. 1877. 
“ crucifm'me (Conrad), Hall. MS., Pal. N. Y. 1877. 
“ “ “ S. A. Miller, in Cat. Amer. Pal. Foss. 1877. 
Glyptodesma erectum (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 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 regularly rounded; anterior side 
broadly convex; posterior side nearly straight or slightly concave. 
Valves very unequal. Left valve varying 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, equalling 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 anteriorly by a distinct 
rounded sulcus, and posteriorly by an interruption and change in the direction 
of the striae, which sometimes produces a defined line of separation. 
Umbonal angle acute. 
Anterior wing auriform and small in young specimens, becoming expanded 
and variously extended in older specimens, limited by a distinct 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. 
20 
