88 THE NAUTILUS. 



crossing the Sieri'a, a little to the south and west of Susanville, the 

 elevation being about 5500 feet which I think is the highest altitude 

 at which any Strepomatid has been collected. 



Both these species have a smooth mantle-margin, G. plicifera be- 

 ing dark slate-color finely dotted with sulphur yellow while in G. 

 nigrina the color is nearly black, inclining to slaty. It is probable, 

 therefore, that all our American Strepomatldw agree in this feature 

 and that as Stimpson supposed we have no typical Melanians with a 

 fringed mantle-edge.' 



An interesting feature in the malacology of this region is the ab- 

 sence of Uiiio from all the streams, though found fossil in the tertiary 

 of this region. I found Margaritana margaritifera of normal form and 

 size abundant up to a height of over five thousand feet above the 

 sea level, in the northern Sierras. At this height it was not accom- 

 panied by Anodonta. 



It is very remarkable that typical Vlvlpara occurs not uncommonly 

 in the Pliocene or possibly the Quaternary fresh water shell-marl of 

 the old Lake beds, both of the Snake River (Oregon) basin and the 

 Lahontan basin (California and Nevada). Why Uuio, Lithasia and 

 Vivipara should have disappeared when their associated Carinifex 

 and Pom'pholyx persist in the same vicinity specifically unchanged, 

 is an inexplicable mystery at present. It shows at least that the 

 West Coast fauna was formerly more intimately connected with that 

 of the eastern region of the United States, than at present. 



Another interesting feature of my visit was the determination, by 

 the aid of the researches of that veteran geologist Prof Thomas 

 Condon of the State University, of the existence of marine Pliocene 

 fossils at Shoalwater Bay, Wash, conformably underlying the qua- 

 ternary and indicating, by the presence of Buccinum cyaneum and 

 other northern forms, at that epoch a colder climate than at present. 

 The most remarkable, and only new form in this bed is a fine 3Iyti- 

 lus as large as 31. califoryiicus but distinguished from all other spe- 

 cies of the genus by its surface which resembles that of il/. edulis 

 superimposed upon which are a few, strong, divaricating ridges ex- 

 tending from about the middle of the valves toward the posterior 

 extreme. 



1 Alcoholic specimens of Western Gomriasis recently examined by me, sent 

 by Mr. E. H. White of Astoria, Oregon, confirm the observations of Dr. Dall 

 respecting the smooth mantle-edge. I hope to figure the dentition later. — Eu. 



