THE NAUTILUS. 5 
richness of color and perfection of form by even the more preten- 
tious members of the genus Cypreea. 
Among the most charming of the 55 or 60 accepted species, O. 
porphyria Lam. (Fig. 3) may be safely reckoned. These are the 
“tent shells” of the amateur collector, being so-called from the 
peculiar patterns which often cover the surface in such profusion as 
to suggest a large military encampment, including the marquees 
supposed to be necessary for official comfort, ete. 
The ground color, on which these tent-like figures appear, is of a 
deep chocolate hue and exceedingly brilliant. Add to this the 
graceful form of the shell and we may readily see that the combina- 
tion presents a picture of the utmost beauty. 
O. eryptospira Ford (Figs. 4, 5) is smaller and less charming in 
appearance than O. porphyria, but the callus-covered spire and 
enamelled body whorl make it a very interesting species. The 
type of this is in my own collection. There is, however, a fine suite 
of typical specimens in the Phila. Acad. Nat. Sciences, and, I 
think, a similar set in the U. S. National Museum at Washington. 
DESCENT AND DISTRIBUTION OF UNIONIDE. 
BY BERLIN H. WRIGHT, PENN YAN, N. Y. 
It must be admitted that the Unionidae are under the same 
natural laws, and occult forces, that have operated for vast ages on 
all animal and vegetal life. Fossilized Unios are found in several 
geological formations, and all living Unios are their descendants, or 
else they are new creations. But no evidence sustains the theory 
of successive creations. On the contrary, we behold everywhere 
successive new but related forms of descent on divergent lines. 
Nowhere is this astonishing fact better exemplified than in the nu- 
merous species of Unionidze. But what causes the new forms? If 
not direct creations—a baseless theory—they are the outcome of 
changed conditions of life or varying environments. 
Geographical distribution furnishes such environments. The 
young fry of the Naiads have a byssus which generally disappears 
early and with this appendage they can and do attach themselves 
to the legs of ducks, wading birds and floating objects. They are 
then easily transported by the semi-annual bird migration, from 
river to river, and from lake to lake, and eventually to very remote 
