CLASS PELECYPODA 
191 
near the cartilage pit; ligament sub-external, marginal, not separated from 
the cartilage. Equals Anatina. 
Type. Mactrd anatina Spengler, 1802. 
Distribution. A single species on each shore of America. 
Range in time. Pliocene. 
Labiosa undulata Gould, 1851. 
Plate 21, fig. 11. 
Proc. Boston Nat. Sci., 4:89; Jour., 6, pi. 15, fig. 7. 
Shell milk-white, fragile, concentrically undulated, ovate, ventricose; 
beaks a little anterior, gaping widely behind; the undulations ending 
abruptly at a posterior, sub-marginal ridge; the undulated portion is also 
minutely corrugated, the wrinkles running from the beaks toward the 
margin; an impressed area in front of the beaks is also destitute of waves; 
anterior half broadly rounded and tumid; posterior half narrowed, com¬ 
pressed and acutely rounded, the superior margin being a rectilinear slope. 
Length, 2^4 inches; height, 2; diameter, 1J4 inches. (Gould.) 
Described as Lutraria undulata Gould. 
Type locality, La Paz, Lower California. 
Range. San Pedro, California, to Panama. In the Pleistocene at 
San Pedro and San Diego, California. 
Genus MACTRA Linnaeus, 1758. 
Shell nearly equilateral; anterior hinge teeth A-shaped, with some¬ 
times a small laminar tooth close to it; lateral tooth doubled in the right 
valve. 
Type. Mactra stultorum Linnaeus. 
Distribution. All seas, especially within the tropics. 
Range in time. From the Lias to the Pleistocene. 
Subgenus Mactrotoma Dali, 1894. 
Mactra dolabriformis Conrad, 1867. 
Amer. Jour. Conch., 3:193. Nautilus, 7; pi. 5, fig. 1. 
Shell triangular, equilateral, slightly ventricose, anterior side somewhat 
produced, subcuneate, rounded at the end; ventral margin regularly 
rounded anteriorly and medially; umbonal slope with a slight carinated 
line, and a distinct fold anterior to it; post umbonal area with an angular 
groove; epidermis yellow-olive, much wrinkled on the carinated line and 
post-umbonal slope; posterior end obliquely truncated, sub-emarginate; 
pallial sinus extends not to the middle of the valve, but opposite the 
posterior end of the fossette. (Conrad.) 
