UNIO. 497 
feebleness of the anterior tooth, but certainly differs from it in the convexity of the 
posterlor margin, which is relatively as much compressed as in the larger ones; it 
shows, however, a feeble indication of the elevated ridge running from the summits 
towards behind and below, which is more developed in U. ostreatus. 
The three older specimens are not only worn and excoriated in places, but they are 
also beset with calcareous incrustations in others, as will be seen by our figure 1. 
ITI, Aroronatas, v. Mart. 
11. Unio cyrenoides. 
Unio cyrenoides, Philippi, Zeitschr. f. Malak. iv. p. 93 (1847) *; Abbild. neuer Conch. p. 79, Unio, 
t. 5. fig. 1°; Kiister, in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Unio, p. 285, t. 96. 
fig. 1 (copy)’. 
Triangular, rather convex, with concentric, somewhat granulated ridges, some of which are irregularly furcated 
or anastomosing ; summits in } of the length; ventral margin much arcuated. 
a. Long. 44; alt. vert. 384, ale 28, diam. 32 millim. 
6 6» 493; 4 37,, 31, 4 26 ,, 
¢. ” 36 ; ” 29, ” 24, ” 19 ” 
a. Philippi’s figure; 6 and c. Specimens in the Berlin Museum, from the Lake of Managua. 
Hab, Crntrat Nicaragua: Lake of Nicaragua (Largilliert 1-8); Lake of Managua (Stold). 
In Philippi’s type the inside is pale red, in the specimens from the Lake of Managua 
itis white. ‘Two of the four examples given by O. Stoll to the Berlin Museum are some- 
what unequivalve, the left valve being more swollen behind the summits than the right, 
which causes an asymmetry in the posterior area. A similar asymmetry is indicated 
by Lea in U. newcombianus and U. gabbianus. 
It is possible that these two last-mentioned species, and some others described as 
peculiar to the said lakes, may prove to be individual variations or local forms of 
U. cyrenoides; but as I have only one specimen of U. newcombianus and none of 
U. gabbianus before me, I am obliged to admit them provisionally as distinct. 
Lake Managua is a little north of the much greater Lake of Nicaragua, and discharges 
its waters into it. 
" 12. Unio newcombianus. (Tab. XXIX. figg. 1, 1a. 4.) 
Unio newcombianus, Lea, Proc. Acad. Phil. viii. p. 103 (1857) ’; Journ. Acad. Phil. (2) iti. p. 314, 
t. 10. fig. 277; Obs. Gen. Unio, vi. p. 82, t. 10. fig. 27°. 
Unio sagrinatus, Sowerby, in Reeve’s Conch. Icon. xvi., Unio, t. 67. fig. 345 *. 
More elevated than U. eyrenoides; ventral margin strongly arcuated, almost iu the shape of a bag; the 
concentric ridges roughly wrinkled ; inside white. 
a. Long. 34; alt. vert. 28, ale 22, diam. 16 millim. 
by, 44; $5 B62, 5:34, ? a 
Go ES 43 32, ,, 28, » 16 5 
a. Lea’s figure; 6. Sowerby’s figure ; c. Specimen collected by Stoll. 
Hab. Nicaragua: without nearer indication of locality (Newcomb ‘~*); Lake of Managua 
(Stol/). 
BIOL. CENTR.-AMER., Terr. and Fluviat. Mollusca, Apri/ 1900. 63 
