Occasional Papers of the Museum of Zoology 19 
let’s description, like so many in the Test. Nov. (1849), was 
totally unrecognizable until 1894, when it was beautifully fig- 
ured, from original specimens, by Fischer and Crosse. How- 
ever, as the general tendency in North American uniones seems 
to be to accept types regardless of the recognizability of the 
descriptions, A. umbrosa will perhaps ultimately become a sub- 
species of A. explicata, as the original naming of the latter 
(1849) has the priority. 
Mesonaias C. and F. (1894) (type U. explicatus Mo.) is 
used here as a synonym of Actionaias. Graphonaias, of the 
same paper, has already been placed in the synonymy of the 
latter by Frierson (1917), who lists the type species (U. medel- 
linus Lea) as an example of that genus. 
From the original comparison, L. sapperi von Ihering (1901) 
appears to resemble an old specimen of dA. explicata, with 
heavier pseudocardinals and obliquely truncate anterior end, 
but the dimensions are those of a more elongate and compressed 
form. The original notes of comparison, without figure, are 
too brief to assure its determination. 
MEASUREMENTS 
3 
S S oy 
Be oo So 
5 OS So 
ame Q 
A. explicata TOME 57) 33 (F. and C., 1894) 
U.alienigenus 82 62 37 (F. and C., 1894) 
A. umbrosa 90 6=— 5g 33 (Simpson, 1914) 
L,. sapperi 114 49 20 (von Ihering, 1901) 
Arroyo Hueyapam: 
Fig. 43 21.5 56(12) 32(7) (smallest juvenile) 
Fig. 44 Aue Or (25) 375) 
Fig. 45 71 62(44) 36(25.5) (compare umbrosa) 
Rio San Juan: 
Fig. 46 94 63(50) 35(33) (male? compare explicata) 
Fig. 47 93-5 62(57.5) 40(37) (female?) 
