HANNIBAL: CALIFORNIAN FRESHWATER MOLLUSCA. 123 



Genus Unio, Retzius. 



Mya (sp.)» Linne, 1758 {M. pictonim, L.) ; Unio, lletzius. 1788 

 {M. pictonim, L.); Lymnium, Oken, 1815 {M. pictorum, L.) ; 

 Unionea, Rafinesque, 1815 (emended form); Mysca, Turtou, 1822 

 {M. pictorwn, L.). 

 Type, Mya pictonim, Linne. 



Shell of moderate size, averaging 60 mm. in length, sub-solid, elongate- 

 elliptical, anteriorly sub-truncate, somewhat pointed posteriorly, 

 slightly indented in front of posterior terminus, umbones small, lying 

 about one-third of distance from anterior end, rather lo\v, and marked 

 by a few doubly looped nodulous ridges, two lateral teeth, and one 

 well-developed and one moi'e or less obsolete pseudo-cardinal in left 

 valve, one lateral and one pseudo-cardinal iu right valve, pseudo- 

 cardinals acicular, lying sub-parallel to hinge ; habitat lacustro- 

 fluviatile. 



Fnio transpacifica, Arnold & Hannibal, n.sp.^ PI. YII, Fig. 18. 



Shell of moderately large size, varying from compressed to somewhat 

 inflated, very similar to U. pictonim, but proportionately broader, 

 particularly in the umbonal region, less distinctly truncate anteriorly, 

 margin of shell slightly sinuate in front of posterior extremity, hinge 

 heavier than in pictonim, a second pseudo - cardinal imperfectly 

 developed in left valve ; habitat apparently lacustrine. 



Type: length 58, breadth 30, depth of valves 20mm. Cotype 

 (cut into exposing hinge in both valves) : length 70, breadth 35, 

 depth of valves 26 mm. 



Eocene : local freshwater beds in Tejon formation of Washington 

 and California. 



Bluifs along Olequa Creek at shoals, one and a half miles above 

 town (types); above shoals two miles above town; bend helow rail- 

 road bridge, one-third mile below town, Little Falls, Washington 

 (H. Hannibal). 



One-fourth mile above Carnegie Pottery plant, in cutting along 

 Western Pacific Railway, Corral Hollow, Tesla, California (^Stanford 

 University Geological Survey, per W. H. Ochsner) (H. Hannibal). 



The first true American Unio known. 



' Unio ' 2)enultinms, Gabb. 



Pal. Cal., i, p. 182, pi. xxiv, fig. 164, 1864. 



Eocene — Tejon formation : coal-mines near ilount Diablo, California. 



"Whatever may be said of this species, the supposed type of which, 

 in a very fragmentary condition, is preserved in the Geological iluseum 

 at the University of California, it is not a Naiad at all. It bears more 

 resemblance to an Anomia than any other genus -which the writer 

 could recall while examining it. 



^ The types of this species, of Viviparus Washingtonianus {Pachychihis 

 Drakei), and of Ambloxus Olcquaensis were obtained by the writer during 

 the summer of 1911 while collecting marine Eocene fossils at Little 

 Falls, Washington, in the interests of Dr. Ralph Arnold. 



