Page:American Seashells (1954).djvu/503

Rh 1½ inches in length, externally very much like a small Mercenaria campechiensis, but not as elongate and with more distinct, concentric riblets. Internally, it is distinguished easily by the extremely small, if not absent, pallial sinus, by the very thick margin of the shell, and in the left valve by the presence of a button-like anterior lateral "tooth." Exterior whitish. Dredged occasionally from 40 to 70 fathoms. Considered a collector's item.

Figure 8 1. Some venerid clams, a and b, Co7npsomyax subdiaphmia Cpr., 2 inches (Pacific Coast); c, Dosmia discus Reeve, 2 inches (Atlantic Coast); d, Aiitigo7ia strigillina Dall, i^ inches (Florida and West Indies); e, left valve of Pitar monhuana Linsley, 1% inches (Atlantic Coast). Ant'igona rugatina Heilprin Queen Venus Plates 38m; 3211 North Carolina to southeast Florida and the West Indies. I to i^ inches in length, rather circular, inflated, and characterized by strong, raised, lamellate, concentric ribs between which are 5 or 6 smaller, raised concentric ridges. Lunule heart-shaped, well-impressed, bordered by a fine, deep line, and crossed by numerous raised threads. Escutcheon well- formed, smoothish. Color cream to whitish with light-mauve mottlings. Very uncommon. Antigona rigida Dillwyn from the West Indies is very similar, but not nearly so obese, and its concentric ridges are stronger and smoother. ^^Chiojiid" Group Ovate-trigonal, inequilateral, sculpture usually cancellate; lunule im- pressed. Inner margins usually crenulate. Teeth strong, without the tiny, pimple-like anterior lateral. Pallial sinus short. This section or group is