PR CEED ING S F THE NA TIONA L MUSE UM. 133 



together with the artificial casts used in the preparation of the descrip- 

 tions and fig'ures. A duplicate set of these casts, however, is deposited 

 in the U. S. National Museum at Washington. 



Class conchifp:ra. 



Family U N i o n i d yi^: . 



TJNIO BARBOURI, new specirs. 

 Plate VIII, Figs. 1, i>, 8. 



Shell elongate-subelliptical, as viewed laterally, narrowly subellipti- 

 cal, as viewed vertically, and ovoid as viewed in front. Dorsal margin 

 gently convex, abruptly rounded to the front margin ; the latter margin 

 gradually rounded to the broadly convex basal margin; posterior 

 margin abruptly rounded or subangular, its most prominent part being 

 above the midheight of the shell; beaks not prominent, situated near 

 the front, but they are not so nearly terminal as is often the case with 

 Cretaceous species of U)iio. Cardinal teeth moderately small; lateral 

 teeth slender; postero-dorsal ridge of each valve slightly prominent and 

 ending, as usual, at the most prominent part of the iwsterior margin. 

 Surface marked by the ordinary lines and imbrications of growth. 



Length, when perfect, of the principal si)ecimen from which the 

 foregoing description is drawn, about 75 mm; height, 35 mm; con- 

 vexity, 25 mm. 



All the known specimens of this species being in the condition of 

 natural molds of the exterior and casts of the interior, the foregoing 

 description, and also the figures illustrating it, have been made from 

 the natural casts and from artificial casts taken from the natural molds. 



One of the artificial casts shows that the beaks had become consid- 

 erably eroded, a condition extremely common in the case of living sjie- 

 cies of Unio in the waters of the Mississippi drainage system, but 

 quite uncommon among North American fossil species of Unto. 



This species has the general shape and aspect of the living Unio 

 miodontoirles Lea, of the Mississipj)! drainage system, and it is in all 

 respects a modern type of Unio. Indeed, it so nearly resembles 

 some individual varieties of the species just mentioned that it is diffi- 

 cult to choose words which shall diagnose it as specifically different. 

 Still, I think it inexpedient, even from a biological point of view, to 

 apply the name of any living species to a Cretaceous form and, that 

 from a geological point of view, it is especially undesirable to do so. 



I have chosen the specific name of this form in honor of Prof. Erwin 

 H. Barbour, of the Nebraska State University. 



UNIO, doubtful species. 

 Plate VIII, figs. 4, 5. 



The collection made by Prof. Hicks contains an internal cast of a small 

 specimen of ?7wJo, probably a young example, which differs too much 



