518 MOLLUSCA. 
Oval, rather thin, and compressed, yellowish-green, with darker green rays ; ventral margin slightly sinuated 
in the full-grown state, straight or even a little convex in the young. Cardinal teeth rather compressed, 
short. Inside shining, whitish, with a yellowish or rosy hue in the centre; in some specimens more 
rose-coloured. 
Long. 57; alt. vert. 26, ale 32, diam. 21 millim. Vertices in # long. 
a. 
b 9» «995 ” 28, ,, 31, 4, 21 ” ” 3 % 
C. » 48; ” 26, 5, 27, 4 17 ” ” 3 ” 
d. ” 46 3 7) 23, ” 24, ” 15 oe) ” 4 29 
& 5 41; ” 23, ,, 25, 4, 14 ” ” + % 
f: » 373 ” 20, , 22, , 13 0 t 
a. From Lea’s figure; d. From Kiister’s figure ; 6, c, e, and f. Specimens collected by H. H. Smith, ¢ and f, 
probably not full-grown. 
Hab. E. Mexico: Rio Medellin, near Vera Cruz (Dr. Burrough?—, H. H. Smith) ; near 
Vera Cruz (Sturm ’, Bennett} 2, Strebel? !). 
In old specimens the summits are somewhat more depressed and eroded, and the 
difference between the height of the summits and that of the wing greater, as in Lea’s 
figure (a): in full-grown, but less eroded, examples this difference is less marked 
(6, c,d); in young specimens (fig. 7) it is again considerable (e, f'), these in the 
Unionide generally having the wing comparatively higher than full-grown ones. 
Hanley’s figure ® is too elongate, probably an inexact reduced copy of that given 
by Lea. | 
U. veracruzensis, Lea, is perhaps the young state of U. medellinus; it often happens 
in this genus, and especially in the present species, that the ventral margin is more 
convex in young specimens than in old ones, 
U. amenus, Lea (Obs. Gen. Unio, iii. p. 39, t. 6. fig. 12), from Texas, is very near 
U. medellinus. 
50. Unio eruginosus. 
Unio e@ruginosus, Morelet, Test. Noviss. i. p. 29 (1849) '; Fisch. & Crosse, Miss. Scient. Mex., 
Moll. i. p. 576, t. 62. figg. 2, 2a, b°. 
Hab. 8.E. Mexico: Rio Michol, at Palenque, State of Chiapas (Morelet 12), 
51. Unio radiatulus, sp.n. (Tab. XXXIX. figg. 8, 8a, b.) 
Shell elliptic, rather thick, concentrically striate, striz flat, but rather broad; yellowish-brown, with several 
(6) dark green rays; fore part shortly rounded; dorsal margin behind the summits at first nearly 
horizontal, then convexly descending ; hinder extremity obtusely beaked and angulated, with a very 
obtuse ridge descending from the summits to the hinder end of the dorsal margin; ventral margin 
straight in the middle, little ascending before and behind. Summits scarcely prominent, in 2 of the 
length. Inside somewhat dull, pale greyish or livid. Cardinal teeth small, somewhat triangular and 
furrowed; lateral lamelle scarcely arcuated. 
a. Long. 44; alt. vert. 243, ale 233, diam. 16 millim. Vertices in 2 long, 
b. 5, 403 ; ” 23, 20, ” 133 ” 9 3 9 
Hab. W. Guatemata: Rio Naranjo, a confluent of the Rio Michatoya, at the station 
Naranjo, and Paso Antonio in the lower part of the Rio Michatoya (Stoll). 
