76 THE NAUTILUS. 



luteola rosacea but differ in the form of the cardinal teeth as well 

 as in the outline of the shell and in the color and texture of the 

 epidermis. 



Oneidensis apparently bears the same relation to radiata that 

 rosacea does to luteola. It is not a depauperate or sporadic form 

 of radiata, for it occurs plentifully and is always recognizable at 

 a glance when mixed with luteola and radiata. A lot of shells 

 from Lower South Bay contained these three mussels in the 

 ratios indicated: oneidensis, 28; radiata, 15; luteola, 16. Indi- 

 viduals occur with a pink shell and nacre like that of the race 

 rosacea. How widely distributed this race of radiata may be is 

 not known but it should be found in other parts of New York 

 State. 



The luteola group of Lavipsilis living in Oneida Lake is of 

 unusual interest from the standpoint of variation. Here the 

 two species have apparently interbred, causing a mixture of the 

 characters of both species. Thus, individuals of radiata occur 

 with a normal hinge but with a polished surface like luteola. 

 Also, luteola individuals occur with a rough surface and the 

 crowded rays of radiata. The breadth of shell in both species 

 varies nearly fifty per cent. All specimens of luteola are more 

 numerously rayed than are those from the West and also those 

 from Western New York, showing apparently a tendency to 

 vary toward the radiata type of surface. A tinge of red is found 

 in individuals of all species, though not as strikingly as in the 

 typical rosacea of DeKay. 



A form of luteola occurs in the lake which is much compressed 

 (resembling in this respect radiata) the epidermis is smooth and 

 the bright green rays are widely spaced. These individuals are 

 noteworthy for^the marked elliptical outline of the shell and the 

 acute V-shape formed by the ventral half of the shell. Meas- 

 urements are given below of these specimens together with 

 typical forms of radiata and luteola. All are males. 



Length 80, width 47, breadth 27 mm. Luteola, compressed. 



" 58, "34, " 19 ram. Luteola, compressed. 



" 64, "40, " 35.5 mm. Luteola, typical. 



" 62, " 38, " S5. 5 mm. Radiata. 



" 80, "25, " 25 mm. i2adm<a, Mohawk river. 



