Occasional Papers of the Museum of Zoology 17 
Actinonaias sapotalensis (Lea) (1841), and approaching 
subspecies computata (Crosse and Fischer) (1893).—Seven 
specimens from Arroyo Hueyapam (H, vii, b); 8 from Rio 
San Juan (H, vii, c). The former include the specimens of 
which the anatomy has been described and figured by Ortmann 
(1912). 
The specimens from the Arroyo Hueyapam are near sapo- 
talensis, while those from the Rio San Juan approach compu- 
tata, which, from the proportions and the figure of the hinge 
armature, appears to be the description of a youngish indi- 
vidual of a considerably larger form, from the Goatzalcoalcos 
River system. One of the larger specimens is arcuate ventrad 
very much like some of the specimens of P. opacata (plate 
VII). In these older individuals, the wavy tendency of the 
rays becomes accentuated towards the ventral margin, until 
they are broken into very pronounced zig-zags, similar to some 
of the species of Plagiola. 
MEASUREMENTS 
5 
= Raney Sel the 
& YG S| @ 
Goi aoe 
a ag ey 2S 
op op s 
Satie. SS 
or ee an) 
A, sapotalensis 56 64 41 - (Simpson, 1914) 
A. s. computata 77 68 39 «6. (C. and F-,, 1894) 
Arroyo Hueyapam 50.5 62 34 (young male) 
53.5 65 39. «© (female) 
Rio San Juan 70.3 67 44 
7950 O50 44 
(largest) 8 65 49 (arcuate ventrad) 
Extremes 50-81 58-67 33-49 
Actinonaias umbrosa (Lea) (1856) and approaching expli- 
cata (“Mo.” C. and F.) (1894). : 
U. alienigenus C. and F. (1893). Plate VII, figs. 43-47. 
Five adult shells and 15 juveniles from the Arroyo Hueya- 
pam (H, vii, b) ; 12 specimens, including odd valves, from Rio 
San Juan (H, vii, c). 
