32 Trans. Acad. Sci. of St. Louis. 



localities can be studied together and adequate comparisons 

 made. 



Palaeoneilo constricta (Conrad)? 



PL IV. f. 20. 



Shell subovate in general outline, sub-nasute behind, from 

 15 to 23 mm. in length, the height about two-thirds of the 

 length, with the highest point in front of the middle. Basal 

 margin regularly rounded from the middle to the anterior 

 extremity and straightened or slightly constricted towards the 

 posterior extremity; posterior margin narrowly rounded; 

 anterior margin more broadly rounded. Hinge-line arcuate, 

 declining more abruptly at the front, marked by numerous 

 crenulations. Valves convex below the beaks, somewhat com- 

 pressed posteriorly. Beaks at about the anterior third, prom- 

 inent, rising above the hinge-line. Umbonal ridge undefined ; 

 an ill-defined depression or broad sulcus sometimes present, 

 extending from just behind the beak to the straightened or 

 sinuate posterior basal margin. Surface marked by fine, reg- 

 ular, thread-like concentric striae which are often obsolete or 

 nearly obsolete upon the posterior portion of the shell. 



Remarks. This species is represented by a considerable 

 number of specimens in the North view collection, and they 

 seem to be closely allied or identical with the New York Ham- 

 ilton species Palaeoneilo constricta. The crenulated hinge- 

 line of the genus is well shown in several specimens, and in 

 form, proportions and surface markings the specimens agree 

 exactly with the illustrations and specimens of the New York 

 shell. P. hedfordensis Meek, from the Bedford shale at Bed- 

 ford, Ohio, is also a closely allied species, and should possibly 

 be considered as identical with P. constricta. It seems, how- 

 ever, to be relatively a shorter shell than P. constricta. 



Palaeoneilo truncata Hall. 



n. IV. f. 21 . 



Shell attaining a length of 30 mm. or more in the largest 

 specimens, length about twice the height. Valves strongly 

 convex, the beaks moderately prominent, rising above the 

 hinge line and situated about one-fourth the length of the 

 shell from the anterior extremity. Basal margin nearly 



