LAMELLIBRANCHIATA. 15; 



GLYPTODESMA, Hall. 



Glyptodesma erectum. 



PLATE XI, FIGS. 1-10; PLATE XII, FIGS. 1-3, 3-9; PLATE XIII, FIGS. 1-4, 1J-I5 ; PLATE XXV, FIGS. U-17 ; 

 PLATE LXXXVI, FIGS. I-S ; .IXD PLATE LXXXVII, FIGS. l-» 



AvicuJa electa, Conrad. Jour. Acad. Nat. Sci., Phila., p. 238, pi. 12, tig-. 5. 1842. 

 " cruciformis, Conrad. Geolog-. Surv. N. Y. : Annual Report, p. 54. 1841. 

 Actinodesma ei'ectuvi (Conrad), Hall. MS., Pal. N. Y. 1877. 



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

 " cruciforme (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, tigs. 



1-10 ; pi. 12, tigs. 1-3, 5-9 ; pi. 13, tigs. 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 ; liasal 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 



