70 University of California Publications in Zoology [Vol. 23 



Biological Survey of San Francisco Bay. — Spirontocaris cristata is 

 essentially a middle and lower bay form (see plate 6). It was taken 

 at somewhat over one-fourth of the dredging stations in both of these 

 sections (21 middle and 10 lower, or 29% and 26% respectively) and 

 at from one-ninth to one-seventh of the hydrographic stations made in 

 the same divisions (12 middle and 15 lower or 11% and 14% respect- 

 ively). In the upper bay it was taken at but one of twenty-two 

 dredging stations (D 5715; 4%) and at only one of eighty hydro- 

 graphic stations (H 5264; 1%). Outside the bay Spirontocaris 

 cristata was taken only at three of the seventeen dredging stations 

 made there (D 5731, 5791, and 5807; 18%). 



The range of distribution within the region covered by the bay 

 survey may be briefly stated, as, from Pinole Point (H 5264) in the 

 upper bay to Point San Mateo in the lower bay (D 5748) and outside 

 to about the 30-fathom line (D 5791). 



From the percentages given above this species is apparently more 

 of a bottom dweller than an inhabitant of the upper water layers, 

 being taken about twice as frequently in the dredge as in the tow-net 

 hauls. With respect to the character of bottom preferred there seems 

 to be little choice as the dredging stations are about equally divided 

 between those with a more or less hard bottom, sand, gravel, shells or 

 rocks, and mud. However, when the average number of specimens per 

 catch is considered, the lower bay with its quite uniformly muddy 

 bottom seems to be the region of greatest abundance. In the lower 

 bay an average of fourteen and four-tenths specimens per dredge haul 

 were taken as compared with two and two-tenths for the middle bay, 

 two for the single haul made in the upper bay, and two per haul for 

 both of the outside stations. This is also shown, though not so strik- 

 ingly, when the tow-net hauls for each region are treated in a like 

 manner, in the lower bay the average number of specimens per catch 

 being four and eight-tenths, for the middle bay three and five tenths, 

 for the upper bay one, outside, none. 



Furthermore, aside from showing that Spirontocaris cristata is 

 found more abundantly near the bottom than near the surface, the 

 averages just given corroborate in another way what has just been 

 brought out, that the muddy bottom of the lower bay seems to be 

 preferred by this species. In the lower bay the highest average per 

 catch is with the dredge hauls while in the middle bay, where the 

 bottom is not so uniformly muddy or not at all muddy in some parts, 

 this relation is reversed, although only to a slight degree, the average 



