Grier: Morphological Features of Mussel-shells. 151 



III. List of Species Employed in this Investigation (43). 



Lake Erie. Upper Ohio. 



Fusconaja flava parvula (Grier). Fusconaja flava (Rafinesque). 



Amhlema plicata (Say). Amblema costata (Rafinesque). 



Pleurobema obliquum pauperculum Pleurobema obliquum coccineum 



(Simpson). (Conrad). 



Elliptio dilatatus slerkii (Grier). Elliptio dilatatus (Rafinesque). 

 Symphynoia costata eriganensis (Grier). Symphynota costata (Rafinesque). 



Anodonta grandis footiana (Lea). Anodonta grandis (Say). 



Parapterafragilis (Rafinesque). Paraptera fragilis (Rafinesque). 



Propter a alata (Say). . Propter a alata (Say). 



Anodontoides feriiss. subcylindricus Anodontoides ferussacianus (Lea). 



(Lea). Eurynia recta latissima (Rafinesque). 



Eurynia recta (Lamarck) . Lampsilis luteola (Lamarck) . 



Lampsills luteola rosacea (Dekay). Lampsilis ovata ventricosa (Lamarck). 

 Lampsilis ovata canadensis (Lea) . 



IV. Physical Conditions and Types of Naiad Faun.b. 



The physical conditions under which the species enumerated in the 

 foregoing list occur may now be discussed. Lake Erie {Cf. Plates I 

 and II, maps) one of the smaller Great (Laurentian) Lakes has a 

 water surface of 9,960 square miles (42). In the part we are most 

 largely concerned with the immediate shore consists of the soft blue 

 Devonian shale named by Newberry (32) the "Erie shale" covered 

 with a varying thickness of drift clay. A large amount of beach 

 debris is annually taken into the water of Lake Erie from this region 

 and almost the entire shore from Sandusky Bay eastward represents a 

 typical beach of sand or gravel, strewn here and there with boulders 

 from the drift-clay above. Especially after storms the streams flowing 

 into the lake are frequently turbid and heavy with sediment, but 

 the St. Lawrence River flowing from the Great Lakes is usually clear 

 and free from all but the finest material in suspension (25). The 

 coarse sediment brought into the lake is swept along the coast by the 

 shore-currents and mingled with the pebbles and sand derived from 

 the wear of the land by shore-waves, or deposited in stratified layers 

 on the lake-bottom. The finer products of the wash of the land or of 

 shore-erosion are thus carried lakeward. In general, the sheet of 

 material thus spread out is thickest and coarsest near the shore, and 

 becomes finer and thinner as the distance from shore increases. The 

 coarse strata in the shore-deposits overlap and dovetail lakeward with 

 the outer layers of fine sediment in the central part of the basin. So 



