670 EXPLANATION OF PLATES. 
PLATE XXVII. 
Figs. 1, 2. Pachychilus liebmanni, Phil. (p. 458), Playa Vicente: 1, adult; 2, not full-grown. 
3-5. érstedi, Mérch (p. 458), Matagalpa, specimens of somewhat different form from 
the same locality. 
6-9. chrysalis, Brot (p. 457), young specimens from Teapa: 6, very young ; 8, nearly 
full-grown. 
10, 11. corvinus, Morel., var. indifferens, Cr. & Fisch. (p. 460), Chiacam: 11 and 11a, 
very young. 
12-14. - chrysalis, Brot, var. nympha, un. (p. 457), Rio Sucio, Salvador. 
15-18. chrysalis, Brot (p. 457), full-grown specimens from Teapa: 15a, operculum. 
PLATE XXVIII. 
[All figures enlarged, the perpendicular line indicates the natural size. | 
Fig. 1. Neritina lineolata, Lam., specimen intermediate between the var. reticulata and the 
var. parcepicta (p. 478), Rio Dulce, 7. 
2. , var. reclivata, Say (p. 472), Tampico, 3. 
3-5. , var. parcepicta, n. (p. 478), Rio Dulce: probably young, 3; 4 and 5, 3. 
6. lineolata, Lam. (p. 471), Lake of Yzabal, $. 
7.— , var. reticulata, Crist. & Jan (p. 473), Lake of Yzabal, 3. 
8. picta, Sow. (p. 589), specimen of normal coloration, Mazatlan, 3. 
9. cassiculum, Sow. (p. 474), Mazatlan, 3: 9a, back view. 
10. picta, Sow. (p. 589), specimen approaching the var. serta, Mazatlan, 3. 
11, 12. virginea, L. (p. 588), specimen of normal coloration, Vera Cruz, 3: 12, with 
rather long white spots below the suture. 
13. 
picta, Sow., var. serta, n. (p. 590), Costa Rica, specimen obtained by v. Seebach, 3. 
PLATE XXIX. 
Fig. 1. Unio newcombianus, Lea (p. 497), Lake of Managua, specimen showing the unequivalve 
summits: 1a, outside; 1] 0, right valve inside. 
2. stolli, n. (p. 492), Rio de Las Salinas, outside and inside. 
PLATE XXX. 
Fig. 1. Unio semigranosus, v. d. Busch, var. testudineus, Morel. (p. 493), Rio Usumacinta, young 
specimen: 1 a, hinge of the left valve. 
specimen intermediate between the normal form and the var. testudineus 
(p. 494), Tampico: 2a and 26, hinge of each valve. 
3. —— —— (pp. 493, 494), Tampico: 3a and 3 8, hinge of each valve. 
4, —— , an old specimen, locality uncertain : 4a and 4 6, hinge of each valve. 
2. 
