6 University of Michigan 
baking the shells to make the quick-lime used to soften maize 
in the preparation of tortillas, the national Mexican bread- 
stuff. The shells from the Laguna de Catemaco (H, vii, d) 
were obtained, through the intervention of the Spanish gen- 
tleman whose hospitality we enjoyed, from a pile (all of one 
species) at the edge of the town of Catemaco. They probably 
came from the mucky-bottomed portion of the shore, near the 
outlet. All of the shells from the Rio San Juan, except the 
one specimen of Anodonta, were bought (for one peso) from 
a peon at the village of Cuatotolapam, on the hacienda of the 
same name. He informed me, through the medium of Mr. 
Thomas La Rue, the subgerente of the plantation, that they 
were obtained, during low water, from a depth of a few feet 
in the Rio San Juan, near the town (H, vii, c). 
UNIONIDAE 
Amblema (Megalonaias) nickliniana ( Lea) (1834).—One 
small left valve, from the Rio San Juan (H, vii, c). Measure- 
ments?: length, 86 mm.; height-index at beaks, 75 per cent 
(64.5 mm.); height-index at wing, 80 per cent (69 mm.) 
diameter-index, 37 per cent (32 mm.). 
From the specimens labeled Q. eightsti (Lea) in the A. N. 
S. P., that form, which Simpson (1914) regarded as a syno- 
nym of Q. heros (Say), resembles some specimens of the latter 
species less than it does Q. nicklimana. At least, it looks as 
if the range of variation in Q. heros, as used by Simpson, is 
1The measurements of the naiades in this paper are given in the 
same order and with the same significance as in Simpson (1914), except 
that, instead of the height and diameter, the height-index and diameter- 
index are given. The index of the height is taken as the height divided 
by the length; that of the diameter, the diameter divided by the length. 
Both indices are expressed as percentages. Except in the case of quo- 
tations, the indices are followed (in parentheses) by the actual dimen- 
sions in millimeters. ‘ 
