174 Trans. Acad. Sci. of St. Louis. 



Dimensions of the type specimen: length llf mm., height 

 8 mm., convexity of one valve 2 mm. 



Remarks. The type specimen which served as the basis 

 for the above original description is the larger one of the two 

 specimens illustrated on the accompanying plate. It is the 

 largest specimen of the species which has been observed, but 

 associated with it are other smaller ones which seem to belong 

 to the same species, and which differ chiefly in having the 

 shell less constricted posteriorly. The species was originally 

 referred to the genus JVucula , but it seems better to transfer 

 it to Palaeoneilo. It is closely allied to P. conslricta of the 

 New York Hamilton fauna. It is also allied to the species 

 from the Vermicular sandstone of North view, Missouri,* 

 which was provisionally identified as P. constricia, and to P. 

 bedfordensis from the Bedford shale of Ohio. 



Palaeoneilo barrisi (W. & W.). 



PI. XV. f. 17-18. 



Palaeoneilo sulcatina, Bull. U. S. G. S. 153: 407. 



Original description. " Shell elongate elliptical in outline; 

 the length twice as great as the breadth ; valves very ventri- 

 cose, most gibbous near the anterior end. Beaks of medium 

 size, situated about two-fifths of the entire length from the 

 anterior extremity ; incurved, not prominent. Hinge-line 

 gently arcuate throughout its entire length ; occupied by a 

 large number of small, curved teeth. Anterior extremity 

 rounded, longest below the middle ; basal margin gently 

 arcuate; posterior extremity obliquely truncate, longest near 

 the hinge line, with a slight emargination below. Umbonal 

 slope slightly prominent, with a gentle depression between it 

 and the cardinal line." 



'* Surface marked by fine, closely arranged, equidistant, 

 concentric lines, which are distinctly undulated as they cross 

 the umbonal slope and the depression above it. Many of the 

 internal casts preserve faint impressions of the concentric 

 lines, except near the basal margin, where they are obscured 

 by the thickening of the shell." 



* Trans. Acad. Sci. St. Louis. 9 : 32. 



