312 PALEONTOLOGY OF OHIO. 



Length of a mature specimen, 1.74 inches ; height to middle of dorsal 

 side, 0.83 inch ; do. to horizon of heaks, 0.87 inch ; convexity, 0.70 inch ; 

 length of hinge line, 1.17 inches. 



This is a very neat, symmetrical species, often found in an excellent 

 state of preservation as casts of the exterior, showing perfectly the form 

 and surface-markings, excepting the' fine granulations usually, if not 

 always, existing in species of this genus. Like some other species of 

 th group, it varies considerably in form, some individuals being pro- 

 portionally shorter and higher than others. In size and general appear- 

 ance it sometimes closely resembles A. clavata of McChesney, from the 

 Chester group. It does not resemble the particular variety of that shell, 

 however, figured hy Prof. McChesney, so nearly as it does what I have 

 always believed to be the usual form of the same ; his typical specimen 

 having the beaks more prominent and farther removed from the anterior 

 end than in the more normal form of the species, and its dorsal outline 

 straighter and more sloping posteriorly, with the valves more compressed. 

 Compared with specimens that I have referred to, A. clavata from the 

 Chester group of West Virginia, collected by Prof. Stevenson, our Waverly 

 species is found to agree very nearly with some individuals of the latter, 

 though it always has its ridges of growth less strongly defined and more 

 irregular, and its anterior basal margin usually more oblique. It also 

 differs in the possession of an obscure anterior umbonal ridge extending 

 from the beaks obliquely backward and downward nearly or quite to the 

 basal margin, a little in advance of the middle. 



The specific name is given in honor of Prof. A. Winchell, the able 

 State Geologist of Michigan, who has described many fossils from the 

 same horizon in the western States. 



Locality and position : Eushville and Newark, Ohio. Upper part of the Waverly 

 group of the Lower Carboniferous. 



Alloeisma venteicosa, Meek. 



Plate 16, figs. 4a, b. 

 Allorisma ventricosa, Meek (1871), Proceed. Acad. Nat. Sci., Philad., XXIII, 168. 



Shell subovate, the 'length being about once and a half the height, 

 moderately convex; posterior margin obliquely subtruncated above, 

 and narrowly rounded or subangular near the middle ; thence curving 

 obliquely under and forward ; base rather deeply and somewhat irregu- 

 larly rounded, the most prominent part being near the middle; anterior 

 side short, with an obliquely truncate or concave forward slope above, to 

 the lower extremity of the lunule, where there is a more or less angular 



