240 University of California Publications in Zoology  [Vou. 14 
3, 4, and 5), and only 9.4 for the gravelly ones. The average for 
sand (group 3) is but 5.4, which is only about one-ninth that for 
pure mud. That such localities are relatively barren of molluscan 
life also appears from the consideration of the average number of 
species per station for group 3. This has been shown above to be 
considerably less than for the other types of bottoms. 
TABLE 7 
PREVALENT SPECIES FOR THE DIFFERENT TyPES oF BoTTOM 
3 Ls} 
i A oe 3 
5 z 8 5 
MRE 3 3 ES 
Ei A cL. iS 8 & & 
eee A A eh te) 
ec WO So. CEA SG aenT 
Cardium corbis Ddic NG AES Chute Gewese SK 
Columbella gausapata x 
TREATING) (ANCE MM OVIS) acct eens eo Pea eg epee eX 
Macoma balthieca ... x x one 
Macoma inquinata .... TE ce gees 
Macoma nasuta Se FO CLK” TET 
Monia macroschisma ... Ge EX 
Mopalia ciliata OK 
Mopalia muscosa ... a x se 
Mya californica nD EG rr eee eX 
Mya arenaria .... x2 aK x es 
Mytilus ecalifornicus ... ee x 
Mytilus edulis aS Goh ce, wp inte >< 
Nassa fossata Beer eG 
Nassa perpinguis ... x 
Nassa mendica — Ba he ek ees 
Ostrea lurida SEC KN BEC SGD I a 
Psephidia ovalis x pac 
Paphia staminea x OK OX 
Petricola carditoides Sea ta 4 
Pholadidea penita : fees 
Saxicava arctica ee ey 2S 
Saxidomus nuttalli .. Ee Ta 
Schizothaerus nuttalli x Kx e 
Siliqua nuttalli eS Eee 
Spisula catilliformis -.. = x 
Solen sicarius Jee 6 SUE ae 
Tellina buttoni was x 
Tellina salmonea x p Seneca PS 
Thais lamellosa Pee ome cath 
Turbonilla franciseana ... et anaes 
SRCVLO GIs yiel yy Se ese renee 2 Xs 
GRATES: (EPI ON ceecereenocscnmcneec teases Gat Jel eat SK 
