91 



The passing of carriages on the street below did not affect these 

 vibrations of the column, for they continued in the same manner 

 "when those vehicles were not passing. While the oscillations were 

 going on, I took a sledge and struck some half dozen blows on an 

 anvil block in the workshop, which did not make any perceptible 

 difference in the movements of the column ; after it had come to 

 rest, the same experiment was repeated, but the column did not in 

 any manner react to the concussion thus produced. 



February 4th, 1861. 

 President in the Chair. 

 Dr. Newcomb presented the following descriptions of new 

 shells. 



Helix Bridgesii. — H. testa profunde umbihcata, depr^sso globosa, 

 plicato-striata et undique minute granulata, sub-diaphana, corneo- 

 grisea intus purpurascenti tincta, centrale linea tenue fuscescenti 

 cincta ; spira sub-conoidea ; anfr. 6. convexis, ultimus antice paul- 

 ulum descendens ; sutura bene impressa ; apertura rotundato- 

 lunaris ; labro expanso, reflexo, pallide lilacino. 



Hab. " San Pablo," Cal. Diam. 27 mill. 



Alt. 19 •' 



Aperturse Diam. 13 " 



Alt. 11 " 



Shell deeply umbihcate, depressly globose, plicately striate and  

 covered with minute granulations, translucent grayish horn color ; 

 within tinted with purple, Avith a narrow, encircling central brown- 

 ish band, spire conical, whorls 6 convex ; suture well impressed, 

 aperture roundly lunar ; lip expanded and reflected of a pale, lilac 

 color. 



RemarJcs. — But a solitary specimen of this shell has been ob- 

 tained ; but it differs essentially from any described species. In 

 its lightness of structure and general aspect it resembles IT. 

 Bonplandii, from which it is widely separated in most of the details 

 of character. It nearest approach to any described California 

 species is to H. ramentosa, (GouH) which is much smaller in size, 

 more solid in structure, with a more depressed spire, lighter color 

 and more scaly granulations. From H. JSiicMiniana, Lea it is read- 

 ily distinguished by its large umbilicus and difference in form. 



It is with pleasure I dedicate this fine species to Thomas 

 Bridges, Esq., of Oakland, an ardent and accomplished naturahst. 



Helix Traskii. — H. testa H. Dupetit Thouarsi Desh. persimilis ; 

 discrepat in eo quod anfr. ultimis non descendit supra ; strias mi- 

 croscopicas numerosas intertextas ostentat. Testa pallido-cornea, 



