OF CONCHOLOGY. 209 



covered a small colony on the "Potreso," a point four miles 

 from San Francisco, and on the west side of the bay, which may 

 have furnished the type of this form, being small and exhibiting 

 its characters more or less strongly. 



A. tudiculata, Binn., 1843. This species, the only one in 

 the Sierra Nevada, has groat extremes of variation in size, oc- 

 clusion of umbilicus and elevation, but the normal number of 

 whorls, 5J, with more or less of the malleated sculpture, are 

 always perceptible. Those found by Voy, in Nevada Co., at 

 about 3/300 ft. elevation, measure, diani. 0-86, axis 0-42. Ex- 

 cept in being slightly malleate instead of reticulated, they are 

 scarcely distinguishable from the specimens of ramentoaa from 

 the Potreso near San Francisco. A few of a still smaller varie- 

 ty, with the umbilicus nearly closed, were found by Harford 

 and Dunn with the dwarf L. Franlcii in the mountains of Mari- 

 posa ; diam. 0*70, alt. 0*38. This form still luis 5J whorls and 

 approaches nearer Carjyenteri as described, than the other form 

 found there though still far smaller and lower in proportion, 

 without revolving grooves. 



In explanation of the reference of this species to the Columbia 

 river in my father's report on the shells in Pacific 11. R. Rept., 

 vol. XII, part 2, 18.59, I think poor specimens of arrosa were 

 found by me near Santa Clara, Cal., in 1855, which might easily 

 have been mistaken for the former, the description of the latter 

 (subnom. aeruginosa) not having been seen. Dr. Gould himself 

 apparently confounded them at first, as he gives tudiculata as 

 collected in " Oregon," by the U. S. Expl. Exped., which did 

 not explore this coast south of Monterey, though possibly they 

 might have found it in the Northern Sierra Nevada. (Brit. As- 

 soc. Rept. 185G, p. 211j. In his description of ceruginosa he 

 points out the differences between the two, (Feb. 1855). 



A. Calif orniensis, Lea., 1839. The original type figured is 

 evidently not the Monterey shell, but the northern form men- 

 tioned by me in this Journal, IV, p. 222, 224, and referred by 

 Dr. Newcomb to Californiensis before he saw the Monterey 

 form. Lea's figure measures, diara. 0-85, axis 0-50, alt. 0-60. 

 The description gives diam. 0-70, alt. 0-60, but as in Nickliniana 

 was apparently drawn from a smaller specimen than that fig- 

 ured, and not very accurately measured either. It is rare near 

 San Francisco Bay and extends north to Klamath Co., (Voy.j 



A. vincta, Val. This is the Monterey shell, which seems to 

 have been considered a more perfect form of the preceding by 

 the Binneys, who figure it under that name. It is much more 

 convex above and below, measuring, diam. 0-90, axis 0*60, alt. 



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