502 MOLLUSCA. 
Var. copanensis,n. (Tab. XXXVI. figg. 6, 6a.) 
Fore part equally rounded above and below, not angulated ; general form a little lower and more elongated ; 
the inside in one specimen bright orange, with a bluish tint in the hinder half; in another whitish, with 
a faint yellowish hue. 
Long. 69; alt. vert. 36, ale 34, diam. 23 millim. Vertices in 3 long. 
Hab. Honpvras: ‘“ Rio Copan, an affluent of the Motagua” (v. Lhering). 
Notwithstanding the difference of locality, the two specimens sent by H. v. Ihering to 
the Berlin Museum agree so well with Fischer and Crosse’s description and figure that 
I cannot separate them as a distinct species; they are, however, much worn outside. 
VI. Nepuronatas, Fisch. & Crosse. 
25. Unio aztecorum. (Tab. XXXVI. figg. 2-40; Tab. XX XVIL. figg. 3, 3a, 6.) 
Unio impressus (Mus. Reg. Berolin.), Menke, Synopsis Moll. ed. 2, p. 107 (1830) (without 
description) ’. 
? Unio emarginatus, Lea, Obs. Gen. Unio, i. p. 174, t. 9. fig. 22 (1833) *. 
Unio aztecorum, Philippi, Zeitschr. f. Malak. iv. p. 95 (1847) °; Abbild. neuer Conch. iii. p. 27, 
t. 6. fig. 2“; Kiister,in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Unio, p. 284, t. 95. 
fig. 6 ° (copied from Philippi) ; Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. p. 607 °. 
Unio plicatulus, Charpentier, in Kiister, Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Unio, p. 154, 
t. 44. fig. 4 (1856) 7. 
Oblong, rounded before and behind, gaping somewhat anteriorly ; dorsal margin arcuated ; ventral margin moré 
or less sinuated ; summits much advanced; pericstracum yellowish-brown or dark brown, in young 
specimens sometimes with greenish rays ; inside purple, in some specimens white; cardinal teeth small, 
triangular, furrowed and crenulated. 
a. Long. 112; alt. vert. 56, ale 56, diam. 423 millim. Vertices in 3 long. 
b. 99 83 > 99 41, 29 42, 99 30 99 39 r 99 
¢. ” 71; ” 31, ,, 35, 4, 20 ” 29 2 PD) 
d. 5 69 ; ) 32, , 36, , 215 ” ry) a ” 
é. 99° 64 5 29 30, 99 32, 99 20 33 99 Pr 99 
f. ” 59 ; 9 29, ,, 380, 4, 20 ” ” a ” 
g ” 513 3 9 26, ” 274, » 16 ” ” 4 ” 
h. ” 50 ) ” 233, ” 26, ” 17 ry 9 a 9 
a ” 48 ; ” 23, ., 26, , 14 ” ’ a ” 
a. Very large specimen from Misantla, collected by Strebel; 6. Large specimen from the same locality ; 
c. A more elongated form, also from Misantla; ¢d. Normal form from Zimapan; e. From Misantla, collected 
by Deppe; f. Measurements of Philippi’s type, according to his figure ; g-i. Younger specimens from Misantla. 
Hab, N.E. Mexico: Zimapan, on the Rio San Juan, southern confluent of the Panuco 
. (Schiede, in coll. Dunker). 
KE, Mexico: Rio de Misantla (Deppe, Schiede, in Mus. Berol.); Playa de Misantla 
(Strebel, in Mus. Hamburg and Mus. Berol.) ; Playa de Nautla (Strebel, in Mus. 
Hamburg); Mexico, without nearer indication of locality (Liebmann). 
The outlines of this species are very variable, as will be seen by the measurements 
