UNIO. 499 
Unio averyi, Lea, Proc. Acad. Phil. 1859, p. 281°; Journ. Acad. Phil. (2) iv. p. 269, t. 44. fig. 149°; 
Obs. Gen. Unio, vii. p. 87, t. 44. fig. 1497. 
Oval-trigonal, swollen, solid, concentrically furrowed ; furrows in the hinder part less impressed; summits 
not very prominent, with minute undulated sculpture, if not eroded; inside white or salmon-coloured ; 
cardinal teeth strong, triangular. . 
a. Long. 41; alt. vert. 283, alee 264, diam. 17 millim. Vertices in 4 long. 
b. % 60; ” 40, 9-30, » Ol $ 
29 ” 3 9 
Hab. S. Panama: Isthmus of Darien (Dr. Caldwell, U.S.N. 1-3); Rio Chumnagua 
(? Chugunagua), on the same Isthmus (Avery 5—*). 
I have no doubt that the two forms distinguished by Lea represent different stages 
of growth of one species, averyi (dimens. 6), being founded on a very old specimen. 
In this genus old examples are often comparatively more swollen than young ones. 
This is the species of “clam” upon which “the ill-fated expedition under 
Lieut. Strain partly subsisted during their journey across the Isthmus.” 
ta 
16. Unio granadensis. 
Unio granadensis, Lea, Proc. Acad. Phil. 1868, p.95*; Journ. Acad. Phil. (2) vi. p. 293, t. 42. 
fig. 103°; Obs. Gen. Unio, vii. p. 53, t. 42. fig. 103°. 
Hab. Cuntrat Nicaracua: Lake of Nicaragua (Bridges 1-3). 
The name of this species, as well as that of Anodonta granadensis, Lea, has been 
taken from the town of Granada, on the north-western shore of the Lake of Nicaragua. 
* 17. Unio aratus. (Tab. XXXIX. figg. 1, 1a, 6, 2, 3, 3.4, 8.) 
Unio aratus, Lea, Obs. Gen. Unio, iv. p. 40, t. 42. fig. 12, vi. p. 83%. 
Unio globulosus, in coll. Dunker’®. 
Of small size, triangularly elliptical, with equal regular concentric ridges ; fore part short, rounded ; hinder 
part elongated, with two ridges enclosing a narrow furrow, descending from the summits to the hinder 
extremity ; ventral margin nearly straight. 
a. Long. 25; alt. vert. 16, ale 13, diam, 13 millim. Vertices in } long. 
b. ” 18; ” id, os LO, ys 8 ” 9 $ ” 
a. Dunker’s specimen ; 6. Lea’s specimen. 
Hab. Cuntrat Nicaragua: Lake of Nicaragua (Lea! ”). 
CrenTRAL AMERICA: without nearer indication of locality (Largilliert *). 
Dunker’s specimen (here figured) agrees so nearly with Lea’s description and figure 
that I think it is a more fully grown or individually larger example of the same species. 
The diameter only being comparatively larger, the shell may be termed inflate, while 
Lea describes it as “‘ rather compressed”; but this difference is often to be seen between 
very old and normal specimens of one species. Lea says :—“‘ Cardinal teeth disposed 
to be double in both valves”; in Dunker’s specimen there are distinctly two cardinal 
teeth, one before and the other behind, in the left valve; and also two, the one above 
and the other beneath, the latter stronger, but separated by a deep horizontal cleft, in: 
the right valve. 
63* 
