THE NAUTILUS. 139 



Genus Phacellozona Pilsbry (new name). 



Synonymy: Angasia Cpr., Table Reg. Chitons, 1873. Dall, 

 Proe. U. S. Nat. Mus., 1881, pp, 283, 286, 289, 290. Pilsbry, 

 Manual of Conchology, XIV, p. 286. 



Not Angasia White, Proc. Zool. Soc. Lond., 1863, p. 498 (Crus- 

 tacea). 



The type of the genus will, of course, reniain Angasia tetrica Cpr. 



Genus Choriplax Pilsbry (new name). 



Synonymy : Microplax Ad. & Ang., Proc. Zool. Soc. Lond., 1864, 

 p. 194. Pilsbry, Manual of Conch.. XIV, p. 21. 



Not Microplax Fieber, Europ. Hem., p. 53, 1861 (Hemiptera). 



Type Microplax grayi Ad. & Ang. This is an extremely peculiar 

 and isolated genus, and forms, !• am disposed to believe, a distinct 

 family of the Eoplacophora 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 Acanthochitidce. 

 The single species was described and illustrated from the unique 

 type in the British Museum, in the Manual of Conchology, vol. XIV. 



DESCEIPTIVE NOTES ON CERTAIN FORMS OF POLYGYRA. 



BY H. A. PILSBRY. 



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. appressa is 

 a snail having the aperture three-toothed, but the upper lip tooth is 

 often small or wanting. It varies toward F. 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, 

 ap2)ressa is not far from the ancestral form from which all the spe- 



