HANNIBAL: CALIFOENIAN FKESHWATEE MOLLUSCA. 133 



For a genus possessing such a fragile shell it is remarkable that 

 Muscidhnn should occur frequently as a fossil. It might be noted 

 that SphcBrium Florissantense, Ckll., of the Oligocene of Colorado, 

 groups here. 



Musculium: lacustre (Miiller). 

 Tellina lamstris, Miiller, 1774; Cijclas Rycl'holti, Kormand, 1841; 

 C. trimcaia, Linsley, 1848 ; C. cardissa, Prime, 1851 ; C. rosacea, 

 Prime, 1851 ; C. securis, Prime, 1851; C. sphcerica, Anthony, 

 1852; SphcBriumlenticula, 'Gould,' Prime, 1862; ? S. Coopen'annm, 

 Prime, 1869 (nude name) ; S. {PrimeUa] Raymondi, J. G. Cooper, 

 1890. 

 Shell of small or moderate size, quadrate-trigonal, inflated in 

 umbonal region, beaks high ; habitat lakes and marshes. 



Palaearctic and jS^earctic Regions. Fraser, Columbia, Klamath, 

 Coast llange, and Mojave Systems. 



Quaternary : Loess of eastern States ; post-Glacial deposits of 

 Vancouver Island. 



MuscuLioii OVALE (Ferussac). 

 Cyclas oralis, Ferussac, 1807 ; C. transiersa, Say, 1829. 



Shell large, elongate-quadrate, somewhat compressed, but varying 

 in this respect, umboues high ; habitat lakes and marshes. 



European and American Provinces, possibly extending into Colorado 

 System. 



MuscuLiTJM paktumeium (Say). 

 Cyclas partumeia, Say, 1822 ; C. elevata, Haldeman, 1841 ; C. Jayensis, 

 Prime, 1851 ; Sphcerium '■patella, Gould', Keep, 1888. 

 Shell large, quadrate-ovate, moderately or but slightly inflated, 

 umbones low ; habitat lakes and marshes. 



Xearctic llegion. Klamath and Coast Range Systems. 

 Quaternary : Loess of eastern States. Miocene : Contra Costa Lake 

 beds, California. 



Family CORNEOCYCLADID^, n.fam. 



Shell small or minute, sub-solid, ovate or trigonal, compressed or 

 inflated, finely concentrically striate, umbones posterior or posteriorly 

 sub-terminal, hinge well developed or more or less obsolete, ligament 

 deep-seated and inconspicuous, pallial line simple; animal herma- 

 phroditic, viviparous; habitat lakes, marshes, streams, and spriugs, 

 less frequently in moist situations. 



The Californian Corneocycladidte belong exclusively to the type 

 and principal group Corneocyclas. Corneocyclas is, however, not 

 coextensive with the old genus Pisidium ; Tellina Henslowiana, 

 Sheppard, of Europe and the eastern States, and Pisidium cruciatiim 

 of Sterki (American Province) belong to Tropidocyclas, a group whose 

 species indicate a radially sculptured stage now outgrown in their 

 phylogenetic histories. 



Many of the members of this family are of widespread occurrence. 

 As frequently happens with microscopic species distributed over 



