/O THE NAUTILUS. 



distinguishing Unio radiahis and Inteolus? The distiuctions do 

 very Avell for some, but to others they seem a good deal mixed. 

 Has not every collector some which he has not named ? " 



After long familiarity with Inteolus in many streams and reservoirs 

 and having several suites of radiatus from different localities, and 

 seeing it plentiful in the Susquehanna River at Muncy, Pa., the 

 thought has not come to me that they were even closely related ; nor 

 do I think they are. Sometimes there is an indescribable something 

 plainl}- discernible to the eye of an expert that separates species, 

 but there is no such difficult or intangible distinction in this case 

 and I think I can make the distinctions plain to Mr. Beauchamp. 



I can emphatically say that I have nothing at all like either species 

 that is not easily named. 



As a first distinction I give the foiin of the female of Inteolus which 

 at maturity becomes very broad and inflated at the posterior end and 

 truncated, while forward it remains narrow and very small, com- 

 paratively. This characteristic I have not seen in radiatus and do 

 not think it exists. The difference between the male and female is 

 so great in Inteolus that Anthony thought them distinct and gave to 

 the male the name of U. distans. 



Another and very marked difference is in the epidermis. In 

 luteolns it is, in its perfect state, polished and hard as glass, giving 

 to the radiating stripes a distinctness rarely seen in the genus. 

 While the lines of growth in radiatus are very much larger, giving 

 the surface to the naked eye moi'e the appearance of velvet or fine 

 plush also giving to the radiating stripes a corresponding dimness. 

 Of course these distinctions in the epidermis come out only in cleaned 

 shells or young specimens naturally clean ; they would not be 

 noticed in mature shells as taken from the water. But even in this 

 state I should readily distinguish either species as it came to the 

 light. If there is such a thing as an intermediate specimen, I 

 should like to see it and would agree to put it in the right place at 

 sight. 



As a third distinction, the range of color in the nacre of radiatus 

 is very great, whilst in luteolus, as far as I have seen, it is uniformly 

 light-blue. I have heard of luteolns with pink nacre but have never 

 seen one. I do not know either whether these two species are ever 

 found together. 



