Grier: Morphological Features of Mussel-shells. 175 



Upper Ohio where the rapidity of the water is greater. It might seem 

 that a shell having an exceptional degree of inflation would be at 

 disadvantage in the short periods during which it might require to 

 move about, for such would offer a greater surface to the water 

 resulting in the impediment of its motions, let alone the obstruction 

 the shell might encounter from a rocky bottom. In the lake, where 

 there is little agitation of the water it might freely expand with less 

 danger to itself. I feel there is something more than speculation about 

 this hypothesis, inasmuch as certain other unpublished observations 

 tend to show that even in rivers the greater degree of inflation is 

 found where the current is less, as is also indicated in the resume of 

 the literature. As to the exception of A. feriissacianus, there is no 

 clue whereby its exception to the law of inflation may be explained. 

 Dr. Ortmann says: "It prefers small streams with sandy bottom and 

 little current, frequently going into lakes." This statement of its 

 favorite life conditions largely recalls Lake Erie. In the years of Dr. 

 Ortmann's collecting (1909-18) he has obtained few or none of this 

 species from the big rivers. Being somewhat primitive in character, 

 it may well have reached in many respects the limit of adaptation 

 compatible with biological balance, and the lake environment does not 

 require the extreme of variation for it in this respect. This has some 

 substantiation in the fact that the tabulation shows it to reach its 

 greatest development in the Upper Ohio Drainage. 



As to the length of the shell, my results corroborate those of the 

 European investigators, who claim that it would be a useful adapta- 

 tion, when connected with other characters, under the conditions of 

 the environment in streams. 



{b) On the Height of the Shell {DVD). 



It was stated in the conclusion that there was a tendency observed 

 for the shells as a whole to be higher in the Ohio. This may be a 

 compensation in growth for the decreased inflation mentioned, or it 

 might be more useful in getting about through the coarser gravel and 

 mud, just as the shape of the more rapidly swimming fishes enables 

 them to cut the water. At any rate this corresponds well with greater 

 length. Fusconaja, L. ovata, and the majority of Proptera were 

 higher in Lake Erie, together with even numbers of other shells. 

 Fusconaja burrows deeply in fine gravel and sand, loves small streams 

 and running water, disliking rough bottom and favors bars of fine, 



