THE NAUTILUS. 



richness of color and perfection of form by even the more preten- 

 tious members of the genus Cyprsea. 



Among the most charming of the 55 or 60 accepted species, 0. 

 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, etc. 



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. 



0. cn/ptoxpira Ford (Figs. 4, 5) is smaller and less charming in 

 appearance than 0. 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 TJ. S. National Museum at Washington. 



DESCENT AND DISTRIBUTION OF UNIONIDJE. 



BY BERLIN H. WEIGHT, PENN VAN, N. Y. 



It must be admitted that the Unionidse 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 Unionidie. 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 



