1918] Packard: Quantitative Analysis of Molluscan Fauna 



321 



Most of the species listed above occur in several groups of quite 

 dissimilar character. This would suggest that the occurrence of a 

 species at a certain locality does not give a true idea of its ecological 

 relationships. The relative abundance of a species within a dredge 

 haul gives a clue as to the optimum environment for that species, and 

 therefore may well serve as the basis for studies in faunal associations. 

 For this reason the average per haul for each species has been calcu- 

 lated. The group in which the highest average falls would appear 

 to represent that type of bottom best suited to the mollusk in question. 

 Such a list is given below. The number of hauls is possibly too few 

 to more than suggest the broad outlines of such molluscan associations. 



The following species -are arranged according to their relative 

 abundance on the different types of bottom : 



Group 1. 

 Living: 

 Dead: 



Group 2. 

 Living: 



Dead: 



Group 3. 

 Living: 



Dead: 



Group 4. 

 Living: 



Dead: 



Group 5. 

 Living: 



Group 6. 

 Living: 



Dead : 



Pure mud 

 None 



Gemma gemma var. purpura 

 Mya arenaria 

 Psephidia ovalis 

 Columbella gausapata 

 Odostomia franciscana 



Mud and sand 

 Cardium eorbis 

 Gemma gemma var. purpura 

 Crepidula nivea 



Pholas pacifieus 



Mud and shells 

 Macoma nasuta 

 Modiolus, cf. rectus 

 Zirfaea gabbi 



Cardium eorbis 

 Zirfaea gabbi 

 Turbonilla franciscana 

 Turris incisus? 



Sand and mud 

 Psephidia ovalis 

 Tellina buttoni 



Mytilus edulis 

 Ostrea lurida 

 Nassa mendica 



Pure mud 



Phaeoides tenuisculptus 

 Turbonilla franciscana 



Sand and gravel 

 Tellina salmonea 



Hinnites giganteus 

 Macoma inquinata 

 Monia macroschisma 

 Saxidomus nuttalli 

 Tellina salmonea 

 Turbonilla keepi 



