28 THE NAUTILUS. 
cular aspect, and in the young are much obscured by the polish of 
the base of the shell; base rounded moderately, about as much as 
the spire, slightly depressed, with a very thin, brilliantly polished 
callus near the axis; aperture with the upper lip projecting consid- 
erably beyond the lower one, moderately thickened and rounded, 
overrunning the keel at the inner corner where there is a narrow, 
sharp sulcus, of which the termination in fully adult shells makes a 
a decided notch in the edge of the lip; lower lip receding, flexuous 
slightly thickened ; throat with three basal, one axial and two par- 
ietal, strong, subequal, spiral laminz, much as in C. salleana, the 
pillar very short, rendered flexuous by the end of the keel; the in- 
ternal walls of the preceding whorls and most of the axis, absorbed. 
Lat. of base (major) 30, (minor) 26, alt. 11 mm. 
Habitat, Pilitla, San Luis Potosi, Mexico, E. W. Nelson. 
This is the finest species of the genus, more evenly divided by the 
keel, more depressed, and larger than C. salleana or C. eolina, the 
only species hitherto known. 
SOME OBSERVATIONS ON THE GENITAL ORGANS OF UNIONIDZ, 
WITH REFERENCE TO CLASSIFICATION. 
BY DR. V. STERKI. 
( Concluded.) 
“ Margaritana.” Considerable changes will be necessary about 
those species hitherto ranged under this genus, and some evidently 
related forms, e.g. Unio pressus Lea and Anod. edentula Say. The 
latter two species seem to stand near Marg. truncata, rugosa and 
complanata. In all of them, the soft parts are of rather the same 
appearance, and especially so are the branchiz, of which the outer 
are gravid, in almost their whole extent, from fall to spring.  U. 
pressus, Marg. rugosa and A. edentula were found with the posterior 
halves of the branchize empty—evidently just emptied, the anterior 
part still filled with young, in spring. Some of them were seen with 
the branchise empty, the gonads charged, in July. 
In edentula, the young are arranged in a singular way, apparently 
different from others. There are small, cylindrical, worm-like, whit- 
ish masses, of about one mill. diameter, lying transversely in the 
branchiz, closely packed together. In them, the young are located, 
six to ten or more in each one, in single or double file, each one in 
