46 THE NAUTILUS. 



Binney and Bland collection seemed hardly quite like 

 ovalis ; small, shiny, thin, rather greenish. 



Of these 33 nominal species of Succinea, possibly not more than 

 about half will prove valid, but it is impossible to arrive at any 

 exact results without further research into the variation, anatomy 

 and distribution of the several forms. 



The distribution, so far as known, present some features of 

 interest. The species of the eastern and northern states are more 

 like those of Europe than the southern or western. The southern 

 and northwestern distribution of the campestres is noteworthy. It 

 appears that in glacial times, owing to a warm current, the coast of 

 Alaska was free from ice, while that of British Columbia was 

 glaciated down to the sea^ ; hence a contingent of the cavipestres may 

 have survived to the north, while their representatives in some of 

 the middle regions were exterminated. 



While on the subject of Succinea, it may be worth Avhile to call 

 attention to fig. 13 of pi. II, Bull, U. S. Geol. Survey, No. 34, 

 (1886). The fossil there figured is referred by Dr. C. A. White 

 with doubt to Limnoea, but is it not a Succinea of the section 

 Lucence f 



Regarding the Calif. Succ. stretchiana (Kaut. VI, p. 72), I fear 

 the specimens were in a box which unfortunately got lost in the 

 post on its way back to Mr. Singley. They seemed to represent a 

 distinct form, but it is possible that they were not true stretchiana. 

 Bland's type was from Washoe Co., Nevada ; and no doubt the 

 specimen from that locality in the Binney and Bland collection 

 belonged to the original lot, the actual type being in U. S. N. M. 

 (see Man. Amer. Land Shells, p. 497). The Washoe Co. specimen 

 examined by me was in some respects like avara, and by no means 

 altogether like the Californian examples ; but considering the 

 variation seen in species of Succinea, I did not feel able to decide 

 without better material, whether they should be held distinct, and 

 so accepted the indication of the labels. There is a Colorado Succi- 

 nea which was formerly thought to be stretchiana, but it is certainly 

 either a var. of avara or a species very closely allied. Is anyone 

 prepared to say exactly what distinguishes stretchiana from other 

 species? If the San Francisco specimens were not stretchiana, I am 

 rather puzzled to know what are the true characters of the species. 

 Perhaps the anatomy would settle the question. 



igee Prestwich, Geology (1888) Vol. II, p. 464. 



