85 

 Stricklandia ? Arachne. (N. sp.) 



Fig. 77. Fig. 78. 



Fig. *I1.— Stricklandia Arachne ; a, ventral view; h, side view; c, ventral valve of 

 another specimen of a somewhat different form ; </, interior of c. All these figures en- 

 larged two diameters. 



Fig. 78. — SI Arethusa; c, interior of a portion of the ventral valve; b, interior of 

 part of the dorsal valve. 



Description. — Semi-elliptical or sub-rhomboidal, hinge line equal to or 

 greater than the width of the shell ; sides converging towards the front, and 

 either straight or gently convex ; front margin rounded, or with a por- 

 tion in the middle straight. Ventral valve strongly convex, sub-pyramidal, 

 greatest elevation a little in front of the beak ; a faint mesial sinus along 

 the middle, not reaching the beak ; area rather large, slightly concave, 

 forming an angle of about 100° with the plane of the lateral margin ; 

 foramen triangular, its width at the base equal to the height. Dorsal 

 valve depressed, convex, with an obscure mesial elevation ; area about one- 

 fourth the size of that of the ventral valve ; foramen open to the beak. 



Surface with obscurely rounded ribs, five or six in the width of one line, 

 these are separated by fine, sharp furrows, and crossed by distinct concen- 

 tric striae, from six to eight in the width of one line, giving to the surface 

 a reticulated appearance. 



The largest specimen seen is 3 lines wide and 2 lines in length. 



In the interior of the ventral valve there is a small triangular chamber 

 beneath the beak, supported by a short mesial septum. In the interior of 

 the dorsal valve there is no mesial septum. 



Locality and Formation. — Point L^vis ; in the upper part of limestone 

 No. 2, Quebec group. 



Collectors. — Sir W. E. Logan, J. Richardson. 



Stricklandia Arethusa. (N. sp.) 



Fig. 78. a, h. 



Description. — Of this species we have only discovered some fragments, 

 but these are quite sufficient to show that it is distinct from any that has 

 been heretofore described. The form appears to be semi-elliptical, both 



