1918] Packard: Molluscan Fauna from San Francisco Bay 257 
Occurrence.—At stations D 5705 (1), D 5709 (1), D 5710 (1, 1), 
Di5t14 (7), Disil5 (2), D'5716 (2), D 5719 (2), D'5720.(5), D'5721 
(10), D 5722 (4), D'5728 (1), D 5726 (2), D 5727 (5, 2), D 5728 (2), 
D 5729 (5), D 5730 (f£.), D 5742 (1), D 5744 (9), D 5748 (f.), D 5749 
(1) DisTbl (6), .DibT52) (6). D'S753 (1), Di57154 (1), D'5755 (1), 
D5i56 (8). Wibtat (i. 5). DibT5s (2). D 5762) (7), D'5764 (77, 13)), 
D 5765 (1), D 5766 (13), D 5767 (24, 1), D 5768 (185, 5), D 5769 (1), 
Dibiiom Gap Dion ion (k)DinitiGn(en1) in oteo (Lb). DBTsil (250), 
D 5782 (162, 1), D 5783 (3), D5784 (105, 1), D 5789 (31), D 5790 
(5), D 5793 (8), D5794 (9), D5795 (1), D5796 (1), D 5805 (2), 
D 5810 (18, 1), D 5811 (6, 36), D5813 (1), D5815 B (38), D 5816 
(24), D 5817 (25), D 5817 A (6), D 5817 B (2), D 5818 A (1), D 5819 
(4), D 5821 A (f.), D 5821 B (f.), D 5822 B (3), D 5828 (1), D 5823 A 
(7), D 5824 A (f.), D5824 B (1), D5826 A (5), D 5826 B (f.), 
D 5830 A (4), D5881 (5), D5832 A (7), D 5883 (2), D5839 (1), 
D 5841 (27), D 5847 (1), D 5848 (1), Standard Oil Pier, Richmond 
(35, 2), Red Rock (85), Key Route Pier, Oakland (62, 1), Cement 
sewer (numerous specimens), Sausalito (31, 1), Bonita Point (72, 1), 
and questionably at D 5739. 
This cireumpolar species, recognized by all conchologists writing 
of this region, is one of the most adaptable of our West Coast mollusks. 
It may be found attached by means of its byssus to almost any object 
in situations ranging from the brackish waters of Carquinez Strait to 
the saline waters of the open ocean. Living specimens were dredged 
in 46 fathoms, but the majority were obtained at depths of less than 
4 fathoms. 
Range—Cireumpolar, Arctic Sea south to San Diego, California. 
Modiolus Lamarek 
Modiolus demissus (Dillwyn) 
Plate 18, figure 1 
Modiolus demissus Dillwyn (1817), p. 314. : 
Modiola plicatula Lamarck, Gould (1841), p. 126; Dall (1889a), p. 38; 
Stearns (1899e), p. 86. 
Modiolus demissus, Sumner, Osburn, Cole, and Davis (1913), p. 683. 
Description.—Gould (1841) described this eastern mussel as follows: 
“‘Shell transversely oblong-ovate, much elongated, narrow before and widen- 
ing backwards, somewhat falciform or arched; beaks moderately prominent, 
not curving outwards, and nearly in contact, very near the anterior extremity, 
which is small and rounded; and the shell is much compressed at this part; 
the lower margin is generally curved or arched upwards, and gaping before 
