68 



Report of the State Geologist. 



al>le that in senile stages it becomes acute, so that the outcome would be large 

 < aiinate shells, such as Mantic. oscy. In this series, however, we lack the con- 

 necting links and the necessary stratigraphic evidence to demonstrate the 

 unity of the two forms. 



It is, to us, more than merely strange that in all our long experience in the 

 acquisition of specimens of this species no large gerontic shells have been met 

 with which can be assigned without reservation to Mcmtic. Pattersoni. With 

 Mcmtic. rhynchostoma the case is otherwise. The concretion-bearing strata 

 along the lake Erie shore in the vicinity of the village of Angola have pro- 

 duced a number of gerontic individuals of great size and excellent preservation. 

 The largest of these measures one foot in diameter, and is more than ordinarily 

 notable for the fact that it displays the apertural margin of the shell without 

 defect. By reference to the figure of this specimen given upon Plate V, the 



Figures 42. 43. Mantieocerut rhynchostoma. Fig. 42, a senile individua\ of 

 volutions, broken through the center, the inner whoils remaining 

 unfractured, showing the rapid narrowing of the final whorl. This figure 

 is one-third the natural size of the specimen. Fig. 4:(, vertical section of »n 

 adult, natural size. 



remarkable character of this aperture will be seen. A pair of broad sagittate 

 lappets extend forward from the lower lateral slopes, terminating in acute 

 points. Above them is a low incurvature of the margin to the venter and at 



