114 



OHIO FOSSILS 



Fig. 310 



Fig. 313 



Of all the winged shells of the Pennsylvanian, 

 Aviculopinna is the most elongate; the length is more 

 than twice the height. The beak is very near one end 

 of the shell. A. american a (fig. 310) is a common form. 



Posidonia (fig. 311) has a rounded outline, very 

 different from that of Aviculopinna and the surface is marked by widely 

 spaced concentric ridges. Two species are common. 



In Myalina (fig. 312) the beak end of the shell is sharply pointed. In 

 some species the wing is distinct, in others it is a mere 

 flattening of the shell behind the beaks. Several species 

 are common. 



Fig. 311 



Naiadites (fig. 313) is a genus of brackish or freshwater pelecypods. 



The specimens from shales are squashed flat and therefore look much Fig 312 



broader than they really were. Uncrushed specimens from iron con- 

 cretions show the true proportions of the shell. It 



has two wings, a small one next to the beak, a larger one at the other end 

 of the shell. It lacks the pointed beak region of Myalina . Two species of 

 Naiadites are common. 



The outline of Entolium (fig. 314) is quite distinct. The ears are 

 prolonged above the hinge line, forming a V with the point at the beaks. 

 We have two common species. 



The following features are characteristic of Pteria (fig. 315): the 

 unequal wings, beak near one end of the shell, elongate outline, and 

 strongly notched larger wing. P. ohioense is common in some beds. 



Aviculopecten (fig. 316) also has un- 

 equal wings but the shell differs from that of 

 Pteria in being as high or higher than wide, 

 not elongate. Several other genera (see 

 below) have about the same kind of outline 

 but the wings are almost equal in size and they have other 

 distinctive features. Four species of Aviculopecte n occur 



Euchondria and the next 

 3 genera have wings of almost 

 equal size but their outline is Fig. 316 

 different. In Euchondria the outline of one 

 wing is concave and the radial ridges have 

 wart-like bumps on them. E. neglecta 

 (fig. 317) is common in places. 



Deltopecten (fig. 318) resembles 

 Euchondria but the radial ridges are 

 smooth or nearly so. Two species of 

 Deltopecten are common. 



Fig. 314 



in our Pennsylvanian. 



Fig. 318 



In Lima and the next genus, the wings are straight or con- 

 vex, not concave. Lima has radial ridges grouped in pairs; 

 they are evenly spaced in Acanthopecten . Lima retifera (fig. 

 319) is common in the Pottsville; it persists into the Conemaugh 

 which also contains another common species of Lima . 



Acanthopecten (fig. 320) may be separated from Lima by 

 ?atures mentioned under that genus. Two species are 

 non. 



Fig. 319 



Fig. 320 



