OF DENISON UNIVERSITY. 7 1 



Sanguinolites naiadiformis , ^^'>n- 

 (Plate IV, Fig. 2.) 



''Length 2I2 the height; laterally flattened below the umbo; 

 dorsal and ventral margins parallel or nearly so, the ventral sometimes 

 with a broad, shallow sinus extending upward over the valves and 

 vanishing near the umbo; a distinct umbonal ridge flattening out near 

 the postero-ventral angle, at which place the outline presents a round- 

 ed angulation ; postero-dorsal slope making with the dorsum an angle of 

 45°. Length 2^ in; height 14-16; thickness ^ in." 



The specimen figured is less typical than others from the free- 

 stone in that it lacks the ventral sinus. Length 75 mm ; height 28 

 mm; convexity 16 mm. 



A variety rather more common than the typical one has the unir 

 bonal ridge more prominent and the anterior ventral curve more con- 

 vex. Several specimens measure about as follows : Length 7^,63, 

 66; height 28, 24, 26 ; convexity 20, 17, t8 ; length of lunule 15, 13, 

 13. This form extends into congl. IL 



A small specimen from the shale below ccngl. I, closely resem- 

 bles the above, but is smaller, measuring 36; height 17; convexity 

 9 (9): lunule 8. Plate IX, Fig. 3. 



Allorlsma (Sangiol/iolttes) nohllis, Dekoninck. 

 (Plate X, Fig. 5.) 



Very large, elongated, expanded and somewhat angulated po.ste- 

 riorly, nearly three times as long as high at the hinge, rather flat, 

 greatest convexity near the middle of the valves. 



Hinge line nearly straight and almost parallel with the very slight- 

 ly curved lower margin ; beak between 1-4 and 1-5 the distance from 

 anterior margin, which is nearly straight and extends a little more than 

 half the height of the shell, forming a rather acute angle ; posterior 

 margin nearly evenly curved or doubly sub-truncate. Surface marked 

 by very strong, irregular, concentric ridges. The post-umbonal ridge 

 is near the hinge and is very slightly elevated, below it are two still 

 fainter ridges passing from the beak to the lower posterior angle and a 



