1906.] NATURAL SCIENCES OF PHILADELPHIA. 141 



may be selected. The study of good series of shells taken at random 

 and not selected shows that all lots of streaked shells are more or less 

 mingled with white ones, and in colonies of toothed shells, fully adult 

 and old individuals may be found without a tooth. On the other hand 

 there seem, however, to be colonies without ragged-streaked individuals, 

 and also communities in which no toothed shells are to be found. 



Perhaps the colonies containing mottle-streaked or toothed individ- 

 uals are mixed or hybrid communities. It is a case where experiments 

 on Mendelian lines by some one on the ground might be productive of 

 valuable results. 



In illustration of the foregoing remarks, a few of the colonies repre- 

 sented in the collection of the Academy may be noticed in more detail. 

 In studying these races it is absolutely essential that the snails be col- 

 lected alive. The colors, particularly of the interior, are evanescent 

 and fade quickly on exposure to the sun and weather, though they 

 change very little if at all in the museum. 



Corpus Christi, Nueces county (pi. VII, figs. 13, 14, 15, 16), collected 

 by J. A. Singley. Of thick-set compact contour, strong, with a thick 

 cream-tinted lip-rib, which is sometimes brown stained. Pinkish 

 white, almost uniform with some very inconspicuous grayish or fleshy 

 streaks. Not one in a lot of 43 is marked with hrown streaks outside. 

 Interior varying from pale yellow to reddish brown, the darker tint 

 exceptional. Columella varying from strongly toothed to nearly 

 straight. Whorls 6, the earliest post-embryonic not distinctly striated. 

 This form is the "binneyanus Pfr. " of Binney, intermedins Singley 

 MSS. of Cockerell. 



Alt. 

 Diam. 



Apertm-e 



At Hidalgo, Hidalgo county (pi. VII, figs. 17, 18, 19), the shells are 

 more slender, white, rarely streaked throughout (fig. 17), but almost all 

 of a series of 41 are variegated on the earlier whorls (fig. 18). Some 

 are strongly toothed, but most shells have no columellar tooth. 

 Interior brown. 



Alt. 30 29.5 29 28.5 mm. 



Diam. 13.5 13.5 13 14 



Aperture 14 14.5 13.5 14.5 " 



A series from Brownsville consists of similar but less elongated 

 shells. 



