1921 J 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 Port 

 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 I14 to Sy 2 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%) 



