1918 | Packard: Molluscan Fauna from San Francisco Bay 273 
Desecription.—This was originally deseribed by Conrad (1837) as follows: 
**Shell suboval, compressed; disks with about eight lamelliform concentric 
slightly reflected ribs, and very obscure radiating sulci; posterior extremity 
widely truncated; color white; palleal impression with a profound sinus.’’ 
Both Cooper and Dall mention this species as occurring on the 
Farallon Islands. It is not found in the Survey collections. 
Range.—Farallon Islands to Lower California (Oreutt). 
Gemma Deshayes 
Gemma gemma (Totten) var. purpurea (Lea) 
Cyrena purpurea Lea (1842), p. 106. 
Gemma gemma, Stearns (1899e), p. 86. 
Gemma gemma, Dall (1902a), p. 401. 
Description.—This variety was described by Lea (1842) as follows: 
*‘Shell rounded-triangular, equilateral, sub-inflated, somewhat thick, pale 
purple and partly white, with transverse striae; beaks prominent; margin not 
crenulated. 
Distinguished from the Venus gemma by its equilateral form and want of 
crenulations on the margin. The beaks are rounded at the summit. It has 
usually a dark purple mark along the posterior margin, which gradually fades 
off, and the anterior portion of the shell is whitish. Occasionally, however, it 
is nearly all purple, but darker toward the posterior margin, and I have one 
specimen which is pinkish. The striae are perfectly regular and at even 
distances.’’ 
Length, 2 to 5 mm. 
Occurrence.—At stations D 5723 (1), D5754 (5), D5771 (1), 
D 5828 A (204), D 5828 B (12), D 5840 (8, 8), north of Key Route 
Pier, Oakland, (2500), and questionably at D 5768, D 5810. 
This exotic species was first reported by Stearns in 1899. It now 
occurs abundantly in the shallower waters within the lower division 
of the bay, occurring also along the eastern shores of the middle 
division. The record of a single specimen from the vicinity of Sausa- 
lito may indicate the present range of the species from the oyster beds 
near Point San Mateo, which represents the supposed center of dis- 
persal for this form. 
Range.—Known only on West Coast from San Francisco Bay. 
Psephidia Dall 
Psephidia ovalis Dall 
Plate 20, figure 4 
Psephidia ovalis Dall (1902a), p. 407, pl. 16, fig. 4. 
Description.—The original description as given by Dall (1902) is as follows: 
“Shell small, white, polished, oval, subcompressed; surface with obsolete 
concentric threads near the anterior base, but over most of the disk smooth; 
