147 



ATHYRIS HEADI. (N. sp.) 



a b 



Fig. 125. Fig. 126. Fig. 127. 



Fig. 125. Athyris Headi. a, dorsal view ; 6, side view of a specimen of the typical 

 form. Fig. 126. a, dorsal view ; 6, side view of a specimen from Lake St. John (var. 

 jl. borealis). Fig. 127. a, dorsal view; &, side view of a specimen from Anticosti 

 var. A. Jlnticostiensis), 



Description. Broad oval or sub-pentagonal ; both valves convex ; sides 

 and front margin occasionally somewhat straight. Ventral valve rather 

 strongly convex, most elevated about the middle or a little above ; beak 

 closely incurved, in contact with the umbo of the dorsal valve ; umbo 

 somewhat carinated ; an obscure mesial sinus which is usually so slightly 

 impressed as to constitute only a flattening of the shell extends from the 

 front margin to within one third of the length from the beak, where it 

 becomes obsolete ; on each side of the sinus the shell descends with a 

 somewhat flat slope to the sides. Dorsal valve not so convex as the ven- 

 tral ; often with an obscure mesial sinus. 



Surface with fine rounded radiating ridges, closely crowded together, of 

 a nearly uniform size, from eight to ten in the width of two lines. 



Length about 10 lines ; width a little less than the length. 



This species is dedicated to the late John Head, Esq., by whose unfor- 

 tunate death science has sustained a grievous loss. 



Locality and Formation. On the south shore of the St. Lawrence 

 opposite Three Rivers. Hudson River formation. 



Collectors. J. Head, Esq., J. Richardson. 



VARIETIES OF ATHYRIS HEADI. 



Var. A. BOREALIS, Fig. 126. This form is found on Lake St. John, on 

 the River Saguenay. It differs from the typical form in being more elon- 

 gate-oval and in having a more tumid umbo. Hudson River formation. 

 Collected by J. Richardson and R. Bell. 



Var. A. ANTICOSTIENSIS. Smaller than the typical form, more nearly 

 circular and with a more tumid umbo. Occurs in the Hudson River for 

 mation near English Head, Anticosti. Collected by J. Richardson. 



