Occasional Papers of the Museum of Zoology 29 
that of A. explicata (Mo.). If this arrangement is correct, 
L. vovirosai Pilsbry shows a much more marked sexual dimor- 
phism than does the latter species, where the female is nearly 
the same shape as the male but is slightly more inflated along 
the posterior ridge and down to the ventral margin. This more 
marked dimorphism and the indications of the beak sculpture 
(even the younger specimens are somewhat eroded) are the 
reasons for the retention of rovirosai in Lampsilis, until the 
soft parts are known. 
MEASUREMENTS 
3 
& = ~ 
Bes oy oe 5 
BB Be 
2 28 38 
eal sl 
oO mt 
jee a 
LL. rovirosat mig Oy 40 (Pilsbry, 1900) 
L, lividus 110 =: 50 (Simpson, 1914) 
Lr. sanjuanensis 
Fig. 39 70.5 61(43) 36(25) (male?) 
Fig. 40 82 65(53) 41(34) (type; male?) 
Fig. 41 co. 6.: 64(58) _ 4440) (female?) 
Fig. 42 98  61(60) 43(42) (female?) 
Extremes (14 
specimenis ) 64-908 58-65 36-48 
Lampsilis ruthveni, new species 
Plate XI, fig. 53; plate XII, fig. 53; plate XIII, figs. 51-54 
Seven specimens, including odd valves (2), from the Rio 
Sam Jcem (isl, with, ©). 
Shell rather small, elliptic to subovate, rather solid, inflated 
behind middle; beaks in front of middle low; beak-sculpture 
not observed ; posterior ridge rounded or shouldered ; posterior 
margin with rounded point at or a little below middle of height ; 
epidermis smoothish, thrown into sulcations and low, rounded 
ridges at growth-lines, dull, golden-brown to dark brown, the 
