70 University. of California Publications in Zoology (Vow. 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- 
tively). 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 
eatch 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 
