510 MOLLUSCA. 
extremity somewhat rostrated and in its lower half perpendicularly truncated. Outside blackish-brown, 
with strong concentric strie ; inside pale purple. 
Long. 131; alt. vert. 82, ale 69?, diam. 40 millim. Vertices in j long. 
Hab. N.E. Mexico: Rio Moctezuma (Dr. Blanding *). 
Lea ? gives “‘ River Moctezuma, Central America,” as locality for this and two other 
species of Unio (U. nicklinianus and U. tampicoensis), but there can scarcely be any doubt 
that the river Moteuzuma, a southern confluent of the Panuco, is meant. Moctezuma 
is the name of a town, a little more to the north, in the State of San Luis Potosi. 
If it were not for the var. connectens, I should treat U. discus as distinct from 
U. panucoensis. 
Var. connectens, nN. 
Unio panucoensis (v. d. Busch), Kiister, in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Unio, 
p. 242, t. 81. fig. 1°. | 
Unio mexicanus, Sowerby, in Reeve’s Conch. Icon. xvi., Unio, t. 55. fig. 281 (1867) °. 
More elongate than Philippi’s type of U. panucoensis, the hinder part of the shell longer and more per- 
pendicularly truncated, the anterior part as in U. discus. Sculpture similar. Inside pale orange or (as 
in the specimen before me) salmon-coloured. 
a. Long. 134; alt, vert. 78, ala 85, diam. 38 millim. Vertices in 4 long. 
b=, ~=—«:180; » 81,,, 71, ,, 41 ,, » 9 
ce 4, 114; om 71,, 66, , ?  ,, » 4 5 
a. From Kiister’s figure; 6. Specimen in the Berlin Museum, from Albers’s collection ; ; ¢. Sowerby’s figure. 
Hab. N.E. Mexico: Rio Panuco, near Tampico (v. d. Busch §). 
Whe Whe 
Probably only an individual variety of U. panucoensis, although the general form 
seems to be rather different at first sight. Kuister § says that the inside is either violet, 
flesh-coloured, or white; but as he does not distinguish this form from typical 
panucoensis, it is not certain whether all these colours are to be found in it. 
The relatively great difference in the height of the wing is due to the fact that in 
Kiister’s specimen the hinder part of the ventral margin is more ascending than in the 
example in the Berlin Museum. 
Var. panucoensis. (Tab. X XXIII. figg. 2, 2a, b.) 
Unio panucoensis, v. d. Busch, in Philippi’s Abbild. neuer Conch. i., Unio, p. 8, t. 2. figg. 1, 2 
(1843) *°. 
Unio lapidosus (Villa, MS.), Kobelt, in Rossmissler’s Icon.:d. Land- und Siissw.-Moll. (2) vi. 
p- 90, t. 176. fig. 1120 (1893) ”. 
Unio discus (Lea), Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. p. 567 (part.) ¥. 
Tnangularly elliptic, much compressed, anterior part (before the summits) projecting, rounded ; ventral margin 
nearly straight at the middle, and almost equally arcuate before and behind; summits in 3-2 of the 
length. Outside brown, with coarse concentric unequal strie ; inside white or pale purple. 
