4 Calvin Goodrich 



cal Tennessee Anculosa. Branches of Black Warrior River, belonging to the 

 Alabama system, and Flint Creek of the Tennessee, both having Anculosae, 

 come within a little distance of each other. If the means of dispersal such 

 as carriage by birds, mammals, wind, tornadoes and such floods as on a 

 plateau bring streams of different drainage systems together — if such means 

 were operative in the case of the Anculosae the forms of the Alabama and 

 Tennessee rivers would long since have mingled. This study has made plain 

 that intermingling has not taken place in recent geological time. 



The manner of life of the Anculosae has undoubtedly had a great deal 

 to do with restricting the means of distribution. I have not visited the 

 Alabama streams and therefore cannot say with exactness just what are 

 the habits of the genus there. It may be supposed, though, that these habits 

 do not differ appreciably from those of the Anculosae of the Tennessee and 

 Ohio systems. In the Clinch and Powell rivers of the Tennessee, the An- 

 culosae are found on stones usually far from the shores and in the strong- 

 est current. The same thing is true of the two species at the Falls of the 

 Ohio. After spring floods a fine coating of silt is left on the stones and in 

 this medium the fresh water animal life leaves the chronicle of its move- 

 ments as plainly as the marks of a pen upon paper Now while Pleurocera 

 and Goniobasis are seen, for mollusks, to move about fairly actively, An- 

 culosa moves scarcely at all. It seems to be content to find a place in the 

 heavy current and to stay there, changing its position little except when 

 change of water level or accident compels it. 



There is not sufficient mud in such locations to serve as a carrier for 

 mollusks on the legs of birds even if the mud present were of the kind to 

 serve that end, which it isn't. As the eggs are laid in the same enviroment, 

 being probably glued to stone surfaces, they too would be little likely to be 

 carried away by birds. If the animal falls and is swept into still water 

 the chances are against its surviving. Logs that might carry Anculosae 

 down stream would come to rest as a rule in the quiet water rather than 

 upon stones in swift water, and falling from such carriers must mean gen- 

 erally that the Anculosae perish. In the light of the record, the chances of 

 such animals changing their habitat from one drainage into another when 

 floods float logs across low land barriers seem exceedingly remote. 



We must understand the dispersal of these creatures to be very slow, 

 very restricted as to means and as being governed very largely by /Changes 

 in the character of a stream — advantageous situations for the life of An- 

 culosae arising and disappearing only over great periods of time. 



The variability of the Pleuroceridae is notorious. Because of this, 

 probably more than for any other one thing, the family has been neglected. 

 Almost everyone who has had anything to do with it has hoped that as 

 collecting became more extensive so many connecting links would be found 

 that the number of species now recorded might be greatly reduced. Almost 

 everyone has tried to avoid adding to the catalogue. One student, bold per- 

 haps but more likely just impatient, did undertake a prodigious labor of 

 lumping and he brought the number of species down to a meager dozen or 

 so — deriving in the end, it must be feared, very little satisfaction for him- 

 self and certainly advancing the knowledge of systematic zoology not a 



