Raymond : 1>rachioi'oL)A and ()sii{ac()da of thk Cha/y. 241 



Genus Heherteli.a Ilall and Clarke. 



24. Hebertella borealis (Billings). 



Orthis borealis Billings, 1859. Canadian Naturalist and Geologist, Vol. IV, p. 436, 



fig. 14. 

 Orthis borealis Billings, 1863. Geology of Canada, p. 129, fig. 56. 



Description. 

 Shell transversely o\al, width at hinge considerably less than the 

 width below. Sides rounded, front straight or slightly rounded. 

 There is a low, broad depression in both valves. The pedicle valve 

 is the more convex of the two in young specimens, but in mature 

 shells the brachial vaKe is slightly the larger. The cardinal area of 



Fig. 13. Hebertella borealis (Billings). A specimen from St. Martin Junction. 

 Natural size. 



Fig. 14. Hebertella borealis (Billings). A specimen with a very short hinge- 

 line. St. Martin Junction. Natural size. 



the pedicle valve is high and incurved, with a narrow delthyrium 

 The surface is marked by from twenty to thirty broad, simple plications,. 

 separated by \evy narrow grooves. 



This species is commonly reported from the Trenton of Canada,. 

 Kentucky, Tennessee, and Minnesota, but the shells so identified 

 have a deeper sinus in the pedicle valve and do not have a sinus in 

 the brachial valve. Professor Foerste has recently given the name 

 Hebertella jrankjortensis to the form which occurs in the Trenton. 

 (Hulletin Denison University, 1909, p. .^18, PI. YH, figs. 11 A, B.) 



