UNIO. | 509 
sculpture and coloration of the umbonal region. The furrow, bordered by two ridges, 
descending from the summits backward, is also visible in U. hjalmarsoni, but in the 
present species it is distinct to near the hinder end in one only of the six specimens 
seen, the furrow, like the radial ridges, scarcely extending beyond the umbonal region 
in the others. 
34. Unio hjalmarsoni. (Tab. XXXVIIL. figg. 11, 11a.) 
Unio lyalmarsoni, Dunker, Malak. Blatt. v. p- 227 (1858) *. 
Rather elongate, elliptic, moderately compressed; dorsal margin before the summits somewhat descending, behind 
them at first nearly horizontal, then arcuate; ventral margin conspicuously ascending in the fore part, 
nearly straight in the middle and hinder parts, the fore half of the shell thus appearing somewhat 
angularly produced, and hinder extremity almest perpendicularly cut off. Summits in one-third of the 
whole length. Concentric plaits over the whole surface, rather strong, close together, some anastomosing. 
Periostracum dirty yellow. Cardinal teeth somewhat thick, oblique, feebly furrowed, and not crenulated. 
Inside bluish-white. 
Long. 36; alt. vert. 183, ale 17, diam. 11 millim. 
Hab. Honpuras: Rio Chamelicon, on the confines of Guatemala (Hjalmarson 1). 
Here figured for the first time, from Dunker’s type, now in the Berlin Museum. 
35. Unio nuculinus. (Tab. XX XIX. figg. 6, 6a, 0.) 
Unio nuculinus, Philippi, Zeitschr. f. Malak. v. p. 176 (1848) *. 
Of small size, elongate, elliptic, pale greenish, with regular strong concentric ridges; fore part somewhat 
produced, hinder part straightly beaked; ventral margin ascending about as much behind as the dorsal 
margin descends, with a narrow furrow descending from the summits to the hinder extremity. Inside 
silvery-white. Cardinal teeth compressed, moderate in size—in the left valve two, one behind the other ; 
in the right valve one, larger, spoon-shaped. 
a. Long. 174; alt. vert. 10, ale 9, diam. 7 millim. Vertices in 3 long. 
b. ” 16; 9 93, ” 1, 2” 7 ” ” 3 ” 
Hab. Nicaracva (Largilliert *). 
Two specimens in the late Dunker’s collection, now in the Berlin Museum. They 
do not appear to be very young, to judge from the solidity of the shell and the extent 
of erosion. ‘The measurements given by Philippi indicate a somewhat greater height. 
VIII. Lampsiuis, Raf. 
36. Unio discus. 
Unio discus, Lea, Trans. Am. Phil. Soc. vi. p. 74, t. 18. fig. 57 (1838)*; Obs. Gen. Unio, ii. p. 74, t. 18. 
fig. 577, and iii. p. 72°; Hanley, Cat. Rec. Bivalv. p. 197, t. 22. fig. 12*; Chenu, Ilustr. 
Conch., Unio, t. 19. fig. 6° ; ? Sowerby, in Reeve’s Conch, Icon. xvi., Unio, t. 62. fig. 310°; 
Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. p. 567 (part.) *. 
Anterior part short, only one-fourth of the whole length, upper anterior margin abruptly descending ; hinder 
