. The Canadian naturalist and geologist. Natural history -- Periodicals. Fig. 14. Fig. 14.—Ortkis borealis. a, rentral aspect; 6, side view ; c, dorsal aspect. Specimens of this species with the surface well preserved are difficult to procure, and I think it highly probable that in many the radiating ridges are subdivided or increase by implantation ; but in the only perfect ones I have seen they are simple quite to the beak. In a specimen nine lines in width there are fifty-one ribs, including the finer ones at the cardinal angles, but the aver- age number is between forty and fifty. This spe
. The Canadian naturalist and geologist. Natural history -- Periodicals. Fig. 14. Fig. 14.—Ortkis borealis. a, rentral aspect; 6, side view ; c, dorsal aspect. Specimens of this species with the surface well preserved are difficult to procure, and I think it highly probable that in many the radiating ridges are subdivided or increase by implantation ; but in the only perfect ones I have seen they are simple quite to the beak. In a specimen nine lines in width there are fifty-one ribs, including the finer ones at the cardinal angles, but the aver- age number is between forty and fifty. This species is somewhat variable in form. Some of the spe- cimens are sub-quadrate, with the cardinal and front angles rounded, the sides being nearly straight, and in these the greatest width is usually near the front. Others have the sides convex, and these have the greatest width about the middle. Often the dorsal valve has an indistinct mesial fold extending from the beak to the front, while others have a slight depression, the effect of which, together with the depression in the ventral valve, is to produce a gentle sinuosity in the anterior margin. In general however, the dorsal valve has neither a mesial fold or sinus, but. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Natural History Society of Montreal. Montreal, Dawson
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