THE NAUTILUS. 139 
Genus Phacellozona Pilsbry (new name). 
Synonymy: Angasia Crr., Table Reg. Chitons, 1873. Dat, 
Proc. U. 8. Nat. Mus., 1881, pp, 283, 286, 289, 290. Prispry, 
Manual of Conchology, XIV, p. 286. 
Not Angasia White, Proc. Zool. Soe. Lond., 1863, p. 498 (Crus- 
tacea). 
The type of the genus will, of course, remain Angasia tetrica Cpr. 
Genus Choriplax Pilsbry (new name). 
Synonymy: Microplax Ap. & Ana., Proc. Zool. Soc. Lond., 1864, 
p. 194. Puirsspry, Manual of Conch.. XIV, p. 21. 
Not AMficroplax Fieber, Europ. Hem., p. 53, 1861 (Hemiptera). 
Type Microplax grayi Ap. & Ana. This is an extremely peculiar 
and isolated genus, and forms, I am disposed to believe, a distinct 
family of the Koplacophora or slitless Chitons—that is, if the slits 
really prove to be completely absent, for the unique type has not 
been disarticulated. In some features it recalls the Acanthochitide. 
The single species was described and illustrated from the unique 
type in the British Museum, in the Manual of Conchology, vol. XIV. 
DESCRIPTIVE NOTES ON CERTAIN FORMS OF POLYGYRA. 
BY H. A. PEBSBRY 
The genus Polygyra is one of the most numerous and characteris- 
tic groups of North American land snails. It ranges over the whole 
of the Eastern United States, from Canada to Florida, and from 
Manitoba to Yucatan, with species in Idaho and on the Pacific slope. 
A few stragglers have reached Cuba, the Bahamas and Bermuda. 
Many of the species exhibit a great amount of variation, and in 
some cases the variations of several allied species form chains of 
mutations almost or quite connecting very unlike species. This is 
the case in the group of Polygyra appressa. Typical P. appressais 
a snail having the aperture three-toothed, but the upper lip tooth is 
often small or wanting. It varies toward P. obstricta var. carolin- 
ensis, which is close to P. obstricta, and less so to P. palliata. In 
another direction P. appressa is allied to P. sargentiana. In fact, 
appressa is not far from the ancestral form from which all the spe- 
