THE NAUTILUS. 87 



given by Mr. Deau are excellent. There is generally that intangi- 

 ble something which is apparent to the experienced eye by which 

 they may be separated, a difference more ]>articiilarly in the texture 

 of the epidermis than anything else ; but even this difference is not 

 always visible to my eyes, and I have handled many specimens that 

 were so puzzling and close that I have been obliged to ask, " Where 

 did they come from?" before ] even dared to guess what they were. 



Generally luteolus is solider, more inflated, wider posteriorly and 

 narrower anteriorly, as well as smoother than radiatus, but not 

 always. A specimen of radiatus in Dr. Lea's collection from Lake 

 Champlain, collected by Dr. Ingalls (Museum No. 85035), is very 

 solid, and as much inflated as U. hydianus, is narrow before, and 

 broad behind, and can only be distinguished from luteolus by the 

 color and texture of the epidermis. 



It was one of the great objects of Dr. Lea in making his collection, 

 to get material from all the different parts of the territory through 

 which the species were distributed, to get all the variations possible, 

 and carefully preserve the name of the collector, and the record of 

 the place in which they were obtained. Had he never done any- 

 thing more than get together in this way this unequalled collection 

 — requiring, as it did, the educating and training of a corps of able 

 assistants in various parts of the world — he would have deserved 

 the gratitude of students of conchology for all time to come. 



In this collection are varieties of radiatus of every possible form, 

 from a great number of localities ; they vary from flattened and 

 almost lenticulai", to oval, quadrate, elongated, obovate and inflated. 

 One of these shells from Newton Creek, N. J. (85058) Avhich is 

 labelled Unio radiatus, has a smooth yellowish epidermis, save 

 when eroded, and I should unhesitatingly pronounce it 3f. luteolus 

 if it had come from Ohio or Indiana. 



Are luteolus and radiatus ever found together ? From the fol- 

 lowing table it will be seen that although JJ. luteolus is a Mississippi 

 drainage species, and radiatus belongs to the Avaters that flow into 

 the Atlantic, the habitats of these species considerably overlap. 

 This last includes only a few of the localities of specimens in the 

 Lea collection. 



Unio radiatus. Unio luteolus. 



Saratoga Lake, N. Y. Niagara Falls, N, Y. 



Troy, N. Y. Mohawk R., Erie, N. Y. 



Little Lakes, Lycoming Co., N. Y. Genessee R., N. Y. 



