676 GEOLOGY OF OHIO. 



The specific name is given in honor of Mr. John Misener of Rich- 

 mond, Indiana, who collected and from whom I received the best speci- 

 mens of the shell seen. 



Formation and Locality : Upper beds of the Cincinnati group, Rich- 

 mond, Indiana, where it occurs in association with Ortonella hainesi and 

 Rliynchonella dentata. 



Ischyrodonta modioli formis, n. sp. 



Plate 54. Fig:. 4-9. 



Shell scarcely attaining medium size, moderately convex, modiola- 

 like, elongate subovate, the base straight or ve^ gently sinuate, the 

 back straight for a short distance behind the beaks, then curving very 

 gradually down into the very obliquely rounded posterior margin ; an- 

 terior end short, sharply rounded, much narrower than the posterior. 

 Beaks small, situated a short distance behind the anterior extremity; 

 both the mesial sulcus and the umbonal ridge are but little developed. 

 The cardinal slope and the posterior part of the surface is marked with 

 rather strong, subregular, concentric furrows, of which from ten to four- 

 teen may be counted in the space of 10 mm. Besides these furrows a 

 set of very fine concentric lines, barely visible to the unaided eye, are 

 to be observed on well preserved specimens. The anterior part of the 

 surface seems to be smooth, the furrows at any rate ceasing suddenly 

 a short distance in front of the middle of the shell. 



In casts of the interior a narrow 7 and more or less distinct umbonal 

 ridge may be traced from the beak to the pallial line a short distance be- 

 hind the center of the cast, while in front of the ridge there is usually 

 a well defined depression or sulcus. Anterior muscular scar strongly 

 elevated, very oblique, sharply defined on the upper side, occupying the 

 greater part of the small anterior end and extending a little posterior 

 to the points of the beaks. Posterior scar very faintly impressed, nearly 

 twice the size of the anterior, situated just within the sloping post-card- 

 inal border of the cast. Pallial line distinct only in the ventral part 

 of the valves. Close to the cardinal border of the casts a long and 

 slightly impressed line represents the support of the internal ligament. 

 Of cardinal teeth there seem to have been but two, one in each valve, 

 the right above the left. The scars left by the small pedal muscles 

 occupy the usual position immediately in front of the cavit} 7 between the 

 filling of the beaks. 



This well marked species, of which I have seventeen speci- 

 mens, is probably nearest /. elongata. It is however a much smaller 

 shell and readily distinguished by its narrower form, more oblique 

 posterior margin, and different surface markings, the concentric 

 lines of growth extending almost uniformly over the w T hole surface in 

 that species. 



In a general way /. modioliforniis greatly resembles several species 

 of Modiolopsis, but that it is not realty related to them is proved by the 



