250 University of California Publications in Zoology  [Vou. 14 
ARCACEA 
ARCIDAE 
Arca Lamarck 
Arca transversa Say 
Plate 14, figures 3a and 3b 
Arca transversa Say (1822), p. 269; Gould (1841), p. 96; Sumner, Osborn, 
Cole, and Davis (1913), p. 684, chart 132. 
Scapharca transversa, Dall (1898c), p. 645. 
Description.—This species is described by Gould (1841) as follows: 
“*Shell transversely oblong, rhomboidal, with from thirty-two to thirty-five 
ribs placed at nearly the length of their own diameters distant from each other. 
Apices separated by a long narrow space, and situated at the termination of 
the posterior (anterior) third of the length of the hinge margin; extremities 
of the hinge margin angulated; anterior (posterior) edge, the superior half 
rectilinear; posterior (anterior) edge rounded; inferior edge nearly rectilinear, 
or very obtusely rounded; on the hinge space, one or two angulated lines are 
drawn from the apex diverging to the hinge edge.’’ 
Length, 12 to 25 mm. 
Occurrence.—At stations D 5781* (4), D 45811 (5), D 5813 (1). 
This species is represented by several old valves obtained from 
three dredging stations at the extreme southern portion of the bay. 
It is an eastern species that has not hitherto been reported from this 
coast. It was probably introduced with the eastern oyster, with which 
it is associated. No living specimens have as yet been obtained, so it 
is not certain that it has gained a foothold in these waters. 
Range.—San Francisco Bay. 
Glycymeris Da Costa 
Glycymeris subobsoleta (Carpenter) 
Axinea subobsoleta Carpenter (1846b) p. 425. 
Description—Professor H. A. Clark of the University of Oregon has kindly 
translated the original Latin description as follows: 
“‘Shell similar to A. septentrionalis, slightly inequilateral, not tumid, um- 
bones obtuse, broad, quite prominent; ash-colored, variegated with reddish 
chestnut; epidermis thick, somewhat laminated; ventral and posterior margins 
quite rounded, anterior margin produced, dorsal straight, sculptured by sub- 
obsolete radiating grooves, often disappearing dorsally; ventral margin strongly 
and anterior and posterior internal margins slightly crenulated; cardinal plate 
subangular, with a few strong, compressed teeth; abductor scar chestnut- 
colored; ligament furrowed.’’ 
This species was not taken by the Survey, although it has been 
reported from the local waters. 
Range.—Vancouver Island to Santa Cruz, California (Orcutt). 
