224 Umversity of California Publications in Zoology [Vou. 14 
at the surface, while nine of them show considerable percentages of 
lime at depths from 40 to 140 centimeters. In the other divisions of 
the bay the tubular samples are, with a very few exceptions, nearly 
uniform in respect to the lime content from the top to the bottom. 
Tn the lower extremity of the bay five of the ten sections show shells 
only. in the middle portion of the sample, indicating a change from an 
unfavorable to a favorable and then back again to a comparatively un- 
favorable environment for the mollusks. At two of the five remaining 
stations the sampling apparatus did not penetrate to the shell horizon, 
which appears to be quite extensive in that region. 
The reason for such fluctuating conditions is not evident. Were 
it not for the bottom stratum of relatively limeless mud the present 
unfavorable conditions might be attributed to some factor introduced 
as a result of the proximity of the cities of San Francisco, Oakland, 
and Alameda. These changes may be due to the variations in the 
silting up of the basin of deposition, whereby during certain periods 
deposition proceeded at too rapid a rate to favor abundant molluscan 
life. Such variations in sedimentation might be expected as a result 
of local diastrophic movements, such as are indicated by changes of 
level registered by the Indian shell mounds around the bay. Or pos- 
TABLE 4 
FAUNA OBTAINED IN CAVITIES IN Rocks at Sratrions D 5845 anp D 5846 
Rock numbers*................. iipee Repo crow rt, tis GQ Yo oO nO Wi ae ae} mt 1G ig iy 
= BS 
oD wo 
4 9 Gu 5 ro a < 
Dimensions in inches ...... x x ms a x x x x = x € x x Eee ae ta 
a 1 = ~ ai) dq oO ct al = (oy Wo} = col oq el 
Weight in pounds -.......... 14% 2 20 2 6% 2%16% 6 6 8% 19 8 5 14% 19% 61% 18% 
Species 
Crepidula nivea —...... ... eRe ee rane 2. 452 oe = 
Entodesma saxicola .... _... Kc ae SE a eee, eee x * 
Kellia lapuerosi .......... -... BO a ded Re Oe Mee! 9K) | SR 
Hinnites giganteus ...... .... ad hued Yee ata i ets ican!» ose 9 Uae ag XS) ct 
Macoma inquinata ..... -... ee eames prin a rt (eee et eee EE oS a) Sates 
Paphia staminea ......... -... ede Pc og 2S Ee FM LOG ASI EN 2 fox 
Pholas pacificus .......... .... Rare CREST GB ea RPA Saree a ENTS Picea Ui ea af eee : 
Pholadidea ovoidea ... .... ee eee em aT fA ee PMS aS ey ecce  Gcot gene sone 
Pholadidea penita ...... .... Peete Ne aNNCCACAD eto) De MEME OM RA UPR)” OE a! cede | O 
Petricola carditoides.. 30s. f= feces eee Ra Troan : 
Ostrea lurida ............... -.. 2 es xs 
Saxicava arctica -....... .... Eee MERI cone OG 3 
Zirfaea gabbi -............. -... x : 
* Rocks 1-6 inclusive; came from station D 5845, the others from D 5846. 
} Living specimens. 
5x44 x 8 
