E. M. Kindle — Bottom Control of Marine Faunas. 451 



ical character of the bottom differs widely. At station 2 

 the bottom is very soft nearly black mud with a large 

 content of organic matter. Stations 6 and 10 have hard 

 bottoms, the materials being chiefly gravel in the case of sta- 

 tion 6, and at station 10 gravel, angular pieces of rock and 

 sand. The bottom of station 3 is allied to that of station 2, 

 but much firmer and comprises a considerable amount of 

 sand. It belongs to the muddy sand type of bottom. Since 

 the different stations differ with respect to factors likely to 

 affect molluscan life only in the character of the bottom, any 

 very considerable differences in the molluscan assemblage 

 which they may show must be ascribed to this as being the 

 only varying factor present.* If the character of the bottom 

 is an important factor in determining the composition of a 

 fauna we should expect the assemblages from the stations with 

 hard bottoms to have a large number of species in common, 

 and the soft mud and hard bottom stations to have very few 

 species in common. Inspection of the following table in which 

 the occurrence of each species in the list is indicated for each 

 station at which it was taken by a check, will indicate to what 

 extent this is true. 



Analysis of Table of Species. 



I am indebted to Dr. Paul Bartsch, Curator of Marine 

 Molluscs in the TJ. S. National Museum, for the determination 

 of the shells listed on the following page. 



This list of 51 species includes three gasteropods which do 

 not appear to have been previously recognized in Canadian 

 waters. These species are : 



Ilyanassa obsoleta Say. 

 Melampus lineatus Say. 

 Tritia trivittata Sa}\ 



All of the other species in the list are recorded by Whiteaves 

 from Eastern Canada.f 



The table shows that stations 6 and 10 furnished each 18 

 species or a total of 22 species. Of the 22 species found at 

 the two stations 13 are common to both stations. In the fauna 

 of either station 72 per cent of the species are common to the 

 fauna of the other station. 



* The influence of decreasing salinity in reducing the abundance of marine 

 life may be observed in ascending the estuaries of streams like the Avon. 

 The discussion of this factor in faunal control is postponed for a future 

 paper. 



fCatalogtie of the Marine Invertebrata of Eastern Canada, pp. 1-272, Can. 

 Geol. Surv., 1901. 



