14 



Fig. 4. " Dorsal view of the same." 



Shell "transversely irregularly ovate; compressed, sub-lenticular; 

 length about twice the greatest height; umbones situated a little 

 behind the mid-length ; ventral margin with a concave notch at about 

 the posterior fom-th of the whole length. In front of this notch the 

 margin is uniformly convex, gradually sloping upwards nearly (if not 

 quite) to the hinge line. The dorsal margin is not perfect in the speci- 

 men figured, but judging from the direction of the striae on the surface 

 of the cast, it is nearly straight, or at the most only slightly convex in 

 front of the beaks, and nearly parallel with the length of the shell, 

 sloping slightly downwards. Behind the beaks it is gently convex, 

 nearly straight, and slopes downwards to the narrowly rounded angle, 

 the latter situated at about one-third the height of the shell. The 

 margin of the beaks is compressed. Close under the beaks, in front, 

 there appears to have been a short escutcheon.* " From the umbones 

 backwards for about six lines, a linear groove runs along close to the 

 dorsal edge on each side. This may be related to the ligament. 



The m^ost projecting point of the anterior extremity appears to be 

 situated considerably above the mid-height of the shell, near the hinge 

 line. The posterior angle is below the mid-height. 



Surface concentrically striated. 



Length, three inches ; greatest height a little in front of the mid- 

 length, eighteen lines ; greatest depth of both valves, just below the 

 umbones, eight lines. 



The specimen was collected by Sii- W. B. Logan in the Upper 

 Silui-ian rocks at Port Daniel on the Bay of Chaleurs." E. Billings. 



Five badly preserved casts collected by Mr. T. C. Weston in 186*7 

 from the Guelph limestones at Hespeler, have been identified with this 

 species by Mr. E. Billings. A single specimen from Elora which is 

 also referable to /. Canadensis, has been forwarded to the writer by Mi-. 

 David Boyle. 



* The word "escutcheon" appears to be here used inadvertently instead of 

 lunule. J. r.W. 



