94 THE NAUTILUS. 



Vitrea nitidula Drap., from Fort Resolution, Great Slave Lake. The 

 name Euconulus trochiformis Montagu is used in place of E. fulvus 

 Miill., in my opinion improperly. The unusual distribution of Suc- 

 cinea grosvenori Lea, from Louisiana to Fort Simpson on the upper 

 Mackenzie, is noticed. I \vas also impressed with the disregard of 

 this snail for altitude or latitude some time ago, when studying the 

 Texan forms, yet could find no character in the shells to separate 

 southern from northern individuals. Succinea chrysis, " the com- 

 monest and largest land shell of the boreal American region," is 

 reported from many places from the Mackenzie river west. A 

 synonym which Dr. Dall seems to have overlooked is S. rotundata 

 Sowerby, Conch. Icon, xviii, pi. 11, f. 78 (1872). This name would 

 have precedence if it were not preoccupied. 



In the Lymnasidae an interesting and valuable discussion of the 

 generic and subgeneric synonymy of the groups is given. No 

 attempt is made to distinguish the races of L. stagnalis, of which 

 several have in recent years been brought into use by some of our 

 students. Lymnsea atkaensis Dall, from Atka, Aleutian chain, is 

 figured. The name of this species was given as atkinensis by Clessin 

 in the Conchylien Cabinet, p. 390. The difficult group of L. mighelsi, 

 emarginata, binneyi, randolphi, etc., is discussed at some length ; and 

 the synonymy given will prove interesting to those who have worked 

 with these perplexing forms. 



The generic and subgeneric synonymy of Planorbis is discussed at 

 length, and long-needed rectifications in the nomenclature are made. 

 Say's original spelling of P, exacuous is restored in place of the 

 emended form exacutus. Planorbis opercularis Gld. includes as 

 varieties planulatus Coop., centervillensis Tryon and oregonensis 

 Van. Planorbis nathorsti Westerl., described from Greenland, is 

 recognized from Labrador. A new section, ffaldemanina, is pro- 

 posed for Segmentina wheatleyi Lea. 



In the Unionidce, the northwestern Margaritana margaritifera is 

 recognized as var. falcata Gld. It differs from the typical form by 

 the purple nacre. It has invaded the head-waters of the Missouri in 

 Montana, and occurs also in Alaska. The new species and varieties 

 are as follows, most of them are illustrated on two handsome helio- 

 type plates : 



Polygyra germana var. megasoma. '' More than four times the 

 size of the typical germana, but otherwise quite similar. Northern 

 California" (p. 26). 



