1895. rnOCEEDINGS OF THE NATIONAL MUSEUM. 385 



Some of the specimens are considerably smaller than the above 

 measurements, a few are a little larger, and a number seem to have 

 beeu somewhat distorted by i^ressure. Specimens AA'hich I believe to 

 be females are fuller in the posterior 

 part of the ventral region than others 

 which may be males. Two casts were 

 found the first year in which collec- 

 tions were made from the . Staked 

 riains, at a windmill three miles north 

 of Dockum, and the name doelnimcnsis 

 was applied to these by Mr. Cummins, 

 though he did not describe the species. '^' 



UNIO DOCKUMENSIS, NEW fiPECIES. 



On making clay casts of some of the 



valves sent, I was convinced that these types were the same as the 

 more perfect specimens, and I have accordingly described the species 

 from some of the latter. 



Locality. — Southeast corner of Garza County, Texas; windmill 3 

 miles north of Dockum ; tank north of Double Mountain River; head 

 of Duck Creek, Dickens County, Texas. 



An abundant and well-distributed as well as quite variable species, 

 of which a large number of examples were sent, generally in fair con- 

 dition, and composed for the most part of crystallized calcium carbonate. 



In form, the species very strongly resembles the European and west- 

 ern Asiatic Unios of to-day, but it is remarkable in being sculptured 

 with strong, radiating ridges on the umbonal area — a character pos- 

 sessed by all the recent South American species, and somewhat imper- 

 fectly by those of Australasia. The teeth, however, are very different 

 from the teeth of these southern forms, and more nearly resemble those 

 of the North American Jurassic and Cretaceous Unios. 



Specimens of what are perhaps two other species were sent, but they 

 are not sufficiently well preserved to describe. 



To sum up, then, these Triassic Unios are evidently not the earliest 

 members of the genus, since they show divergent characters, which 

 are dominant in Avidely distributed and prominent groups of this genus 

 found living at the present day. Thus Unto graciliratus in its some- 

 what broken and radiating lines possesses characters now found in an 

 assemblage of peculiarly sculptured species of eastern Asia, and the 

 teeth of U. subplanatus have characters like those of all or nearly all 

 the species of the southern hemisphere. The radial beak sculpture is 

 unknown at the present day outside of South America and Australa- 

 sia, while the forms of at least three of these species, as well as their 

 interiors, where exhibited, bring to mind most strongly the species 

 which now inhabit Europe and western Asia, and a small group belong- 

 ing to the Mississippi area. 

 Proc. N. M. 95 25 



