UNIO. 503 
and figures: in normal full-grown specimens of moderate size, as well as in most 
young ones, the height of the summits is distinctly less than half the length ; in very 
old examples, however (as in a and 5), the height of the summits is about half the 
length, though it is possible to see, by the lines of growth, that the same specimens, 
in a younger state, were also comparatively lower. Young specimens are not 
distinctly sinuated at the ventral margin. Generally, the colour is dull, without 
lustre, but very young examples (i) are of a shining yellow-brown. 
Unio emarginatus, Lea, according to the description and figure, agrees fairly well 
with large well-sinuated specimens of U. aztecorum; but as Lea did not know the 
locality of his species, I refrain from using his name. 
In the late Dunker’s collection, now in the Berlin Museum, there are two examples, 
labelled “ Unio purpuriatus, Say, Mexico, Anthony,” which agree very well with 
smaller scarcely-sinuated specimens of Unio aztecorum. Say’s description also, 
“. . . basal margin a little compressed in the middle, and sometimes almost com- 
pressed in that part,” agrees better with U. aztecorum than with U. medellinus ; but 
as the American conchologists refer Say’s name to the latter, I dare not contradict 
them. At all events the name purpuriatus, Say, cannot be used for any American 
species of the genus, being preoccupied by Lamarck in 1819. 
Var. strebeli. (Tab. XXXVII. figg. 1, La, 2, 2a.) 
Unio strebeli, Lea, Proc. Acad. Phil. 1866, p. 183°; Journ. Acad. Phil. (2) vi. p. 318, t. 51. 
fig. 131°; Obs. Gen. Unio, xii. p. 78, t. 51. fig. 181°; Fisch. & Crosse, Miss. Scient. Mex., 
Moll. ii. p. 594”. ' 
More abbreviated, the height of the summits being more than half the length of the shell. 
a. Long. 94; alt. vert. 49, alee 50, diam. 33 millim, Vertices in ? long. 
b. ry) 73; a) 42, ,, 39, 5, 24 ” ” 4 9 
Hab. ¥:. Mexico: Playas of Misantla and Nautla, with the typical form (Sérebel, in 
Mus. Hamburg and Mus. Berol.); Vera Cruz (Strebel &1'), 
This seems to be an individual variation, chiefly occurring in large-sized specimens, 
rather than a geographical variety, Strebel’s examples from Misantla having been 
collected apparently with the normal form. Lea mentions two diverging raised lines 
descending from the summits towards the hinder extremity, but, according to his figure, 
these must be very obtuse and blunt, as they can be seen in almost every species of 
the genus. 
Var. soledadensis. 
Unio soledadensis, Crosse & Fisch. Journ. de Conch. xli, p. 111 (1893) *; Miss. Scient. Mex., 
Moll. ii. p. 608, t. 69. figg. 3, 3a, 6”. 
Summits somewhat less advanced. 
Hab. E. Mexico: Soledad, State of Vera Cruz (Sallé 3? 18). 
