1918] Packard: Molluscan Fauna from San Francisco Bay 285 
obliquely truncated, rectilinear; beaks central, ligament margin arcuate; tooth 
much dilated, oblique; colour white; palleal impression without a sinus, but 
forming a right angle posteriorly.’’ 
Length, 7 to 25 mm. 
. Occurrence.—At stations D5700 (2), D5701 (1), D5702 (2), 
5705 (2; 1), D 5708 (3), D5710 (5), D 5712 (9), D 5713 (3), D5714 
(GY), ID ales (4) IDV aialiss (ab), ID SyAl) (ah), IDSYERISGye IDeyeee (G2) 
D 5726 (8), D 5727 (4,11), D 5731 (5) D 5732 (4), D 5739 (6), D 5740 
(4), D 5741 (1), D 5742 (25), D 5748 (2), D 5744 (4), D 5745 (21), 
D 5747 (2, 2), D 5752 (2, 3), D 5753 (1), Di5754* (5), D5755 (2), 
D 5757 (1), D 5762 (5), D5763 (6), D 5764 (3), 5765 (4), D 5767 
(4), D 5768 (3), D5771 (2, 9), D5772 (1, 5), D572 (2), D 5778 
(45), D 5779 (51), D 5784 (8), D 5795 (3), D 5796 (10), D 5798 (14), 
D 5800 (2), D 5808 (1), D5817 A (9), D 5818 (1), D 5818 A (10), 
D 5818 B (3), D5819 A (6, 2), D5820 A (1), D5821 A (28, 14), 
D 5821 B (23), D 5822 A (10), D 5822 B (114, 12), D 58238 A (16,11), 
D 5823 B (2, 2), D 5824 A (6, 23), D 5824 B (390, 1935), D 5825 (18), 
D 5825 A (1, 87), D 5825 B (26), D 5826 (1), D 5826 A (195), D'5826 
B (3), D 5827 A (5), D 5827 B (3), 5828 (1, 1), D 5828 A (1), D 5828 
(414), D 5829 A (4), D5882 A (46), D 5833 (2, 5), D5834 (25), 
D 5835 (1), D 5836 (1), D 5841 (13), D 5847 (1), D 5747 B (8), Key 
Route Pier, Oakland (12), Sausalito (9), and questionably at D 5787, 
D 5794, D 5831. 
This prevalent species was taken by the Survey both from the bay 
and open ocean. Its distribution differs from that of the preceding 
species in that old shells occur more abundantly within the Golden 
Gate and adjacent waters. It is not improbable that strong currents 
of the Golden Gate transport these light shells from the shallower to 
the deeper waters. 
Range—Chichagoff Island, Alaska to Topolobampo, Mexico (Dall). 
Mya (Platydon) cancellata Conrad 
Plate 29, figures 2a and 2b 
Mya cancellata Conrad (1837), p. 236, pl. 18, fig. 2. 
Platyodon cancellatus, Carpenter (1863), p. 637; Dall (1898¢), p. 858; 
Arnold, R. (1903), p. 179. 
Description—This species was originally described by Conrad (1837) as 
follows: 
‘*Shell subelliptical, ventricose, with numerous prominent, slightly undulated 
concentric striae; a slight furrow extends from beak to base; posterior side with 
radiating striae; obsolete, or wanting on the posterior slope; umbo prominent; 
posterior side short; cardinal tooth very erect, dilated, bimarginate.’’ 
