Occasional Papers of the Museum of Zoology 19 



let's description, like so many in the Test. Nov. (1849), was 

 totally unrecognizable until 1894, when it was beautifully fig-- 

 ured, from original specimens, by Fischer and Crosse. How- 

 ever, as the general tendency in North American uniones seems 

 to be to accept types regardless of the recognizability of the 

 descriptions, A. umbrosa will perhaps ultimately become a sub- 

 species of A. explicata, as the original naming of the latter 

 (1849) has the priority. 



Mesonaias C. and F. (1894) (type U. explicatus Mo.) is 

 used here as a synonym of Actionaias. Graphonaias, of the 

 same paper, has already been placed in the synonymy of the 

 latter by Frierson (1917), who lists the type species (U. medel- 

 llmis Lea) as an example of that genus. 



From the original comparison, L. sapperi von Ihering (1901) 

 appears to resemble an old specimen of A. explicata, with 

 heavier pseudocardinals and obliquely truncate anterior end, 

 but the dimensions are those of a more elongate and compressed 

 form. The original notes of comparison, without figure, are 

 too brief to assure its determination. 



Measurements 



