127 



the surface, departing from it, and rendering the whole exterior 

 minutely and beautifully cancellated. The shelf on the left, or 

 coiumeliar side is not simply a partition, as in Crepidula or Navi- 

 cella^ but a true columella, and if broken transversely across, 

 shows an entire volution of the shell around it. At the upper 

 termination of this columella is always found a small notch or 

 canal, and at the anterior extremity is a shallow canal as in Con- 

 cliolepas. In short, its structure and habit seem to be those of 

 the shell well known as Purpura monodoiita, Quoy, or P. madre- 

 porarum^ and which Dr. Gould refers to the genus LeptoconcJius, 

 (Mollusca of Exploring Expedition.) Whatever may be the 

 true genus, Dr. Gould thinks these two shells are clearly allied. 

 Until further light, however, he would prefer to have it retain- 

 ed under Svvainson's genus, and called Pedicularia decussata. 

 Shell small, solid, irregular, in general elongated oval, with a 

 prominent obtuse apex on the upper third of the left side, inclin- 

 ing laterally. Surface finely decussated with concentric or radi- 

 ating lines; outer lip thickened, and somewhat revolute ; inner 

 lip sharp, straight, with a submarginal groove. Length, ^ inch. 

 Breadth, ^ inch. 



Dr. Gould also communicated a description of several 

 new species of land and fresh-water shells, as follows: — 



NEW SPECIES OF LAND AND FRESH-WATER SHELLS FROM WEST- 

 ERN (n.) AMERICA. 



Helix ^ruginosa. Testa globoso-conica, solidula, umbilicata, 

 indentata et minutissime granulata, coloribus rufo-olivaceis et 

 flavis variegata et fascia fusca cincta ; anfractibus 7 convexis : 

 apertura rotundato-ovata ; labro reflexo, incarnate ; fauce livida. 

 Diam. If poll. ; axis f a -^^ poll. Brought from San Francisco 

 by Dr. Bigelow. 



Has the general form and coloring of H. Townsendiana^ Lea, 

 and the aperture of H. tudiculata, Binney. The former has a dif- 

 ferent aperture, revolving strioe, and is destitute of a band ; the 

 latter is not umbilicated ; and neither have a granulated surface. 



Helix infumata. Testa magna, discoidea, biconvexa, ad 



