294 • MEMOIRS OF THE CARNEGIE MUSEUM. 



Remarks: The distinctness of this species from L. luteola has been much 

 discussed. Some writers (Dean, 1891) hold that it is sharply separated, while 

 others, among them Simpson (1891), admit that there apparently are intergrades. 



According to my experience I must say, that I never had in our state any 

 trouble in distinguishing the two species. L. radiata is more compressed, lacks 

 the shining epidermis, often hag reddish nacre, and the difference between the male 

 and the female shell is considerably less marked than in L. luteola. 



But I possess a few specimens which indeed are somewhat abnormal. This 

 applies chiefly to some I received from C. H. Conner, and which come from Newton 

 Lake, Camden Co., New Jersey. These are more swollen than the normal form, 

 and in the female the shell is more expanded in the postbasal region, and in shape 

 they thus greatly resemble L. luteola. However, even in these specimens the epi- 

 dermis has the fine wrinkles of L. radiata, and is not smooth and shining as it is 

 in L. luteola. I think that these specimens represent the reaction of L. radiata to 

 the lake-environment. 



With respect to shape and principally color, this species appears to be quite 

 variable outside of Pennsylvania, but within this state it is rather uniform. It 

 seems to me that in the northern parts of its range lighter epidermis (yellow to 

 light brown) prevails, while farther south darker tints (dark green to brownish) 

 are the rule. In the extreme south (southern Virginia and North Carolina) this 

 species seems to develop a distinct local race (var. conspicua (Lea)). 



It should be mentioned, that L. radiata to a certain degree resembles Acti- 

 nonaias ligamentina in general shape and color, and the dark green specimens 

 with broad rays distuictly recall the latter species. Such specimens may be recog- 

 nized by the more elongated shape, thinner shell, and by the rough epidermis. 

 Likewise the presence of pmk in the nacre, and the beak-sculpture serve to dis- 

 tinguish them.^^^ 



Of course, the examination of the soft parts always shows that these two species 

 have no close genetic relationship. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Delaware River, Yardley, Bucks Co. 



Schuylkill Canal, Manayunk, Philadelphia Co. 



Susquehanna River, Selinsgrove, Snyder Co. 



West Branch Susquehanna River, Williamsport, Lycoming Co. (D. A. Atkinson). 



North Branch Susquehanna River, Tunkhannock, Wyoming Co. 



^^ A specimen from Grand Rapids, Michigan, in the Carnegie Museum, was labeled U. radiatus, 

 and, has indeed, much external resemblance to this. But closer inspection has shown that it is Adinonaias 

 ligamentinn, having the smooth epidermis and the beak-sculpture of tliis species. 



