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HANNIBAL: CALIFORNIAN FKESHWATEH MOLLUSCA. 135 



!Mull.), in synonymy; Fisiim, Gray, 1847 {T. anmiea, MiilL), not 

 Pisum, Megerle, 1811 ; Cordula, Leach, 1852 {T. amnica, Miill.) ; 

 ^ Musculium, Link,' H. & A. Adams, 1857 {T. amnica, Miill.); 

 Fluminina, Clessin, 1873 {2\ amnica., Miill.). 



Type, Tellina amnica, Miiller. 



Siib-genus Pisidium. Shell small or minute, ovate, rather com- 

 pressed, umbones lovr, somewhat posterior and naked, hinge well 

 developed, cardinal teeth small and usually joined above in right 

 valve, the anterior transverse, the posterior sub-parallel to hinge, 

 laterals short and weak ; habitat chiefly in rivers. 



Sub-genus Corneocyclas, s.s. Shell similar to preceding but trigonal, 

 umbones elevated, posteriorly sub - terminal, hinge rather poorly 

 developed, teeth sub-obsolete ; Pisidium stage usually completed in 

 or shortly after leaving the marsupium (species which pass the 

 Pisidium stage in the marsupium are frequently caliculate, due to 

 the abrupt change in mode of growth) ; habitat lakes and springs, 

 uncommonly in streams. 



Corneocyclas (Pisidium) pulchella abdita (Haldeman). 



Pisidium ahditum, Haldeman, 1841 ; P. uUramontamim, Prime, 1865 ; 

 P. Angelicum, Howell, 1865; P. nivale, Westerlund, 1885; 

 P. Randolphi, Roper, 1895; P. Rowelli, Sterki, 1903 ; P. ahditum 

 Huachucanum, Pilsbry & Ferriss, 1906. 



Shell of moderate size, rather narrowly ovate and pointed anteriorly, 

 compressed, beaks inconspicuous, hinge moderately developed ; habitat 

 streams, forms intergrading ia^ixxiS. pulcliella in lakes and springs. 



Palfearctic and IS'earctic llegions, Mexican Province. 



Quaternary : Loess of eastern States ; Summer Lake beds, Oregon. 



Intergrading forms between this sub-species and pulchella are 

 abundant and often hard to place. 



Corneocyclas (Pisidicji) Meeki, n.sp. Pi. VI, Fig. 12. 

 ? Sphcerium rvgosum, Meek, 1877 {pars). 



Shell large, broadly quadrate-ovate, moderately compressed, beaks 

 low, hinge well developed ; habitat apparently lacustrine. 



Length 11, breadth II, depth of valve 3 mm. 



Eocene : Truckee Lake beds, jS'evada ; Payette Lake beds, Idaho. 



Hill near Hawthorne on the Belmont stage-road, Nevada. 



A lai'ge species recalling C. (P.) amnica, but broader, more convex, 

 and rather quadrate in outline. 



Not recognized by subsequent writers : 

 Pisidium Sibericum, Clessin, 1870. 

 Siberia; Port Clarence, Alaska. 



Pisidium horealis, Clessin in Westerlund, 1890. 

 Siberia ; Port Clarence, Alaska. 



