1895. PROCEEDINGS OF THE NATIONAL MUSEUM. 335 



that there is some little doubt as to whether the strata in which they 

 were found is Triassic or Jurassic. 



Something like a year ago a half dozen species of fossil Unios were 

 sent to the writer by Mr. E. T. Dumble, of the Geological Survey of 

 Texas, which came from what are believed to be fresh-water Triassic 

 beds in that State. Numerous valves of one of the species show per- 

 fect cardinal and lateral teeth, which do not seem to difler from those 

 of many recent species.' These six forms, though not particularly 

 striking in outline or appearance, belong to at least as many different 

 groups, and do not show any more relation to each other than a half 

 dozen specimens would if taken at random from different parts of the 

 world. One of them is somewhat triangular in outline and compressed, 

 with cardinal teeth much like those of the South American forms; 

 another has slight, radiating striie on the posterior part, and a third 

 species, which resembles some of the forms of U. pictorum of Europe, 

 has strongly developed^ radial beak sculpture ! The fact of this diversity 

 would go to show that the genus had been, in all probability, a long 

 time established at the time these were living. A few species have 

 been found in the Jurassic beds of the western United States, some 

 of which seem to be prophetic of groups which are living to-day in the 

 Mississippi Valley, and the forms which are known to be Cretaceous 

 from that region bear out this prophecy. But when we come to the 

 lacustrine or estuary strata of the Laramie group in this same terri- 

 tory, we find a most astonishing resemblance to forms now occupying 

 the central United States. These beds are believed by some to be 

 Upper Cretaceous; by others they are referred to the Lower Eocene, 

 and Dr. White, whose labors in this field are so well known, believes 

 that the waters in which they were deposited were slightly brackish ; 

 and in fact the Unios and other fresh-water shells of that region are 

 often found associated with Cyrena, Ostrea and Anomiaj genera which 

 now live in estuaries. 



In the Laramie beds, species are found evidently belonging to such 

 groups as that of Unio pUcatus, U. perplexus, U. yibbosus, U. clavus^ 

 U.meta7iever, JJ.securis, U. alatus, and Anodonta grand is, and there are 

 forms from these strata which could hardly be separated from living- 

 species if the latter were fossilized. Dr. White has called attention to 

 the fact^ that the anterior jjortion of many of the elongated species of 

 these beds is greatly shortened, and this character is observable in a 

 number ot species in China. Whether the Naiades originated in North 

 America or the Old World is not now known. At any rate, I do not 

 think any careful student can examine a good series of species from the 



'These species were sent to the writer to be named aud described, and a paper was 

 prepared with de.scriptioos aud tigures, to be jxibiislied iu the report of the Geolog- 

 ical Survey of Texas. On account of the lack of appropriations for continuing the 

 work, the paper was not published by the Survey. The National Museum has under- 

 taken its publicatiou, aud it will shortly appear iu the present volume of I'rocecd- 

 ings (pp. 379-383). 



-Third Auu. Kept. U. 8. (Jeol. Surv., p. 431. 



