45 Ithaca Group 45 



occasionally in the Ithaca group. 



Aviculopefien riigcestriatus? Hall. 



A few specimens which are found in the Portage and Ithaca 

 groups are doubtfully referred to this species. 



Aviculopecten lautus var. ithacensis n. var., PI. i, fig. 3. 



The specimen on which this varietj' is based differs from A. 

 lautus, figured by Hall, in having the beak prominent, the 

 hinge line much shorter than the width of the shell, very dis- 

 tin(5t concentric striae, and only a portion of the strong rays with 

 intermediate finer ones. 



The left valve has a width of nine-twentieths and a height 

 of two-fifths of an inch. 



From the Portage at the foot of Ithaca falls. 



Aflinopteria sp. 



Specimens of this genus are common through the Ithaca group 

 and upper Portage. Prof. Hall has described ten species of 

 ABinopteria from Ithaca. These probably represent variations 

 of two or three species. All I have seen I have been able to 

 refer to the three following species: — 



Afiinopteria tenuistriata Hall. 



A few specimens from the Portage and the lower part of the 

 Ithaca group are referred to this species. 



A£linopteria boydi Hall. 



Typical specimens of this species are abundant at Triphammer 

 and other localities in the upper Ithaca fauna. 



Afiinopteria perstrialis Hall. 



Specimens referred to this species are common in the Portage 

 and Ithaca rocks. 



The points of difference made by Hall between his Ithaca 

 species of Afiinopteria, are shown in the following synopsis of 

 their characfters: — 



Analytical key to the species of Aflinopte7'-ia. 



A. Body nearly erecft, broadly ovate; hinge line extended. 



A. Concentric striae crenulating the rays and bending back in 



the interspaces. Afiinopteria seta. 



A' . Concentric striae not crenulating the rays nor bending back 



in the interspaces; form quadrate. A. tenuistriata. 



