92 LAND AND FRESH WATER MOLLUSKS 



cotypes, now in the National Museum, makes it evident that Dr. 

 Gould was right in referring this form to P. dilatatus Gould, 1841 (not 

 Pfeiffer, 1841 *), or dilatus Haldeman, 1844. To this latter form, in 

 my opinion, should be united, as local races, P. buchanensis Lea, 

 1844, and P. alabamensis Pilsbry. The young of P. exactions Say 

 frequently approach dilatatus, but the latter can usually be distin- 

 guished by its axial height being greater, its columella more vertical, 

 and the substance of the shell, especially in southern specimens, more 

 thick and solid. The aperture of the adult dilatatus is usually dis- 

 tinctly thickened by a deposit of callus, but in exacuous I have never 

 observed more than a very thin wash of shelly matter around the open- 

 ing. I have spelled the name of this species as Say did in two sepa- 

 rate works ; as he gave no derivation it seems to me we have no right 

 to correct his spelling on purely theoretical grounds. 



Planorbis (Menetus) opercularis Gould. 



Planorbis opercularis GOULD, Proc. Boston Soc. N. Hist., n, p. 212, 1847; 

 Moll. U. S. Expl. Exp., p. 113, Atlas, figs. 132, 132, o-, 1852 (Sacra- 

 mento River, Calif.). 



Planorbis planulatus COOPER, Rep. Nat. Hist. Wash. Terr., p. 378, 1859 '< 

 Pacific R. R. Rep., xn, p. 378. BINNEY, Land and Fw. Shells N. Am., 

 pt. n, p. 126, fig. 209, 1865. 



Planorbis centervillensis TRYON, Mon. Fr. Univ. Moll. U.S., 



p. 57, Planorbis, pi. vil, figs. 7-9, 1872. 

 Planorbis opercularis var. oregonensis VANATTA, Nautilus, 

 ix, p. 53, Sept., 1895 ; not P. oregonensis Tryon, 

 1865. 

 Planorbis callioglyptus VANATTA, Nautilus, ix, p. 54, 1895. 



Range. San Francisco and northward, west of the 

 Sierra Nevada. 



Type form : California ! Oregon ! Washington 

 near Seattle ! 



Variety planulatus W. Cooper : Whidbey Island, 

 Puget Sound ! Shawnigan Lake, Vancouver Island ! 

 FIG. 71. Plan- Seattle, Wash. ! Freeport, Wash. ! Victoria, B. C. ! 

 orbisopercularis C bell > s Creek R C . ! Pender Island, B. C. ! 

 Gould (typical). T ^ . , 



Atka Island, Aleutians, Alaska, near Korovm Bay ! 



Variety centermllensis Tryon : Alameda, Calif. ! Noyo River, 

 Calif. ! San Leandro, Calif. ! Oregon ; Unalaska Island, Alaska ! 

 Variety oregonensis Vanatta : Salem and Portland, Oregon ! 



*I learn through Prof, von Martens that Pfeiffer 's species was published in 

 the double part v-vi, of the Archiv fur Naturgeschichte, either in the last part 

 of 1841 or the early portion of 1842, so that Gould's priority is certain. 



