LAMELLIBRANCHIA TA. 
265 
GOSSELETTIA, Barrois. 
Gosselettia triquetra. 
PLATE XXXI, FIGS. 9-17; and PL4TE LXXXVII, FIG. 12. 
Pterinea triqueter, Conrad. Geolog. Surv. N. Y.: Ann. Rept., p. 116. 1838. 
Mytilarca triqueter (Conrad), Hall. Prelim. Notice Lam. Shells, etc., p. 22. 1869. 
Gosselettia triquetra (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 31, 
figs. 9-17. Jan., 1883. 
Shell of medium to large size; body triangular, oblique; in young shells the 
height and length are nearly equal, in older shells becoming more elongate; 
anterior margin truncate, flattened on the ventral side; posterior margin 
broadly rounded. 
Valves equal, very convex, sub-angularly gibbous along the ventral side. 
The convexity or breadth of the closed valves is about equal to the height 
of the shell. Ventral side vertical. Dorsal side sloping very abruptly in 
young individuals, and less abruptly in older shells. 
Hinge-line straight, nearly or quite equalling the height of the shell. 
Beaks anterior, strong, elevated and incurved. 
Test thick, marked by fine concentric lines of growth which are crowded 
and much elevated on the anterior side. In older specimens the striae 
become irregular and lamellose toward the basal margin. 
Ligamental area comparatively wide and very finely striated longitudinally. 
Cardinal teeth three, strong and somewhat diverging. Lateral teeth elongate 
and extending nearly to the posterior extremity of the hinge-line. The 
anterior muscular scar is sub-circular, deep, situated hear the inner border of 
the cardinal plate and truncating the anterior cardinal tooth. 
A medium-sized specimen has a length of 58 mm., height 43 mm., breadth 
41 mm. A larger individual has a length of 80 mm. and height 55 mm. 
The older shells present some similarity to M. ( Plethomytilus ) oviformis, but the 
ventral angular slope is characteristic. In young specimens the triangular and 
extremely gibbous form distinguish it from all other species here described. 
34 
