1921] Schmitt: The Marine Decapod Crustacea of California 275 
Biological Survey of San Francisco Bay.—Regarding the occur- 
rence of this species Dr. Rathbun (1884, p. 765) says, ‘‘H. oregonensis 
is especially abundant in muddy sloughs of salt or brackish water 
where it literally swarms. Hundreds of uplifted threatening claws. 
welcome the intruder who ventures near the mud flats when the tide 
is out.”’ 
In view of these remarks our shore collections, which were confined 
to the middle bay, constitute a very imperfect littoral distribution 
picture. Four specimens were taken among the rocks at Point Bonita 
between tide marks, thirty at Sausalito, one at Tiburon in a 150-foot 
seine, twelve from the piles of the Key Route pier, eighty-three on 
the mud flats north of the Key Route pier, thirty-four along the Rich- 
mond shore north of the Standard Oil pier, and twenty-five among 
rocks on Red Rock. 
However, when the dredging records are consulted we find that 
Hemigrapsus oregonensis was taken very much more frequently in 
the lower than in the other divisions of the bay (see plate 10). It is 
in the lower bay that the muddy bottom preferred by this species 
predominates. Here it was taken at sixteen stations (80%), of which 
the greater number, eleven, were recorded as more or less shelly 
as they were principally in oyster-beds; but it must be remembered 
that in the lower bay these shelly bottoms are primarily mud bottoms 
(Townsend, 1893, p. 348, 350). The other five stations from the 
lower bay were on a pure mud bottom in three cases, on muddy sand 
in another, and on an uncharacterized bottom at the remaining one. 
In the upper bay this species was taken at but two (10.4%) of 
the stations, both of which (D 5817, 5819) were made with the sledge 
trawl off Point Pinole on a somewhat gritty mud bottom; for the 
middle bay we likewise have only two records (10%), dredged in-shore 
with the launch off Point San Quentin on an uncharacterized bottom 
(D 5750), and along the south side of Golden Gate, inside of Fort 
Point (D 5778), on a bottom largely made up of ‘‘fine, clean, gray 
sand and medium sized rounded stones.”’ 
The average number of specimens per haul in the lower bay was 
sixteen and eight-tenths as compared with one and five-tenths speci- 
mens per haul for the upper and middle bays. The greatest number 
of specimens taken at any station was one hundred and two dredged 
in 114 to 314 fathoms (D 5768) off Alameda, in the upper part of 
the lower bay. Seven (35%) of the total number of dredging stations 
made in the bay were in less than 2 fathoms of water, only five (25%) 
