3Iodiolopsis modlolar 



IS. 



140 



tory, and at a very early age has developed a remarkable taste for 

 natural science. 



The specimens were found in the excavation for Columbia avenue, 

 about 150 feet above low water-mark. Not observed elsewhere so far 

 as known. 



UocUolopsis modiolaris — (Coxrad, 1838). 



Somewhat obliquely oblong ovate, narrowed before, expanded and 

 obliquely truncated posteriorly ; basal margin usually contracted or 

 slightly arched upward ; cardinal line extended straight or slightly 

 curved ; beaks moderately prominent near the anterior extremity ; an 

 oblique, scarcely defined ridge, extending to the posterior basal mar- 

 gin ; surface marked by concentric undulations ; muscular impression 

 distinct, close to the anterior extremity. 



The hinge line of this species and the internal markings never hav- 

 ing been illustrated, I have caused to be engraved the following figure: 



Fig. 17. Hinge line and internal structure of Modiolopsis modiolaris. 



The hinge line is toothless, and marked by a ligamental depression, 

 commencing justanterior to the beak and extending to the posterior part 

 of the shell The external ligament was situated between and anterior 

 to the beaks, and extended posteriorly to the end of the hinge line. 

 The muscular impression is circular and deep, and situated immediately 

 below and subanterior to the beak, and not anterior to it, as appears in 

 the cast. A mesial ridge extends from the beak to the base of the 

 shell, separating the muscular impression from the umbonal cavity. 

 Pallial line distinct, and marked by irregular pits. 



The beak of the shell scarcely extends lieyond the hinge line, and is 

 less prominent than it would appear, judging from the cast alone. 



This siDecies is quite common on the hills back of Cincinnati, and has 



