114 CONTRIBUTIONS TO CANADIAN PALEONTOLOGY. 



Strophodonta plicata, Hall. 



Slrophodonta plicata, Hall. 1860. Thirteenth Rep. N. York St. Cab. Nat. Hist., 



p. 90. 

 " 1867. Pal. State N. York, vol. IV., pt. 1, p. 144, pi. 

 63, figs. 30-32. 



Near Thedford, Eev. J. M. Goodwillie, 1882: one rather small but 

 very characteristic specimen. 



Spirifera subdecussata. (N. Sp.) 

 P). 1,5, figs. 3 and 3 a. 



Shell somewhat compressed, the maximum thickness through the 

 closed valves being a little less than one-half the greatest length of the 

 ventral valve : lateral outline tivansversely rhomboidal or obscurely 

 ^jentagonal, but with the front margin nearly semicircular : breadth a 

 little greater than the length : greatest breadth at the hinge line, 

 whose extremities are angular. 



Ventral valve considerably elevated at the umbo : cardinal margins 

 diverging at an angle of about 132° : mesial sinus broad and shallow, 

 especially at and near the anterior margin : area large, ascending and 

 obliquely flattened, rather more than one-fourth as high as broad and 

 transversely striated, pseudo-deltidium also large, its breadth at the 

 base nearly equalling its height. 



Dorsal valve very moderately convex, with a bj'oad, low, rounded 

 mesial fold, which is most strongly defined on and at the anterior margin. 



Surface ornamented by about fifteen low, rounded ribs on each 

 side of the mesial fold and sinus. The central portion of each valve 

 is quite devoid of ribs, but the whole surface is faintly and concentrically 

 striated, and the ribs on the lateral areas are marked with exceedingly 

 minute and closely arranged radiating linos. 



Dimensions of the only specimen collected : maximum length, thirty- 

 eight millimetres ; greatest breadth, forty-five mm. ; approximate thick- 

 ness through the closed valves, eighteen; height of hinge area in the 

 ventral valve, twelve; breadth of pseudo-deltidium of the same at its 

 base, eleven. 



Banks of the Thames Eiver, Moraviantown, Eev. J. M. Goodwillie 

 1882 : one imperfect and not very well preserved specimen. 



The shape and coarser markings of this shell are extremely like 

 those of the S. aspera of Hall,* from " calcareous shales of the age of 



* Geol. Iowa, Yol. I., part 2, (1858) p. .508, pi. 4, figs. 7 :i, b, c, J. 



