388 CONTRIBUTIONS TO CANADIAN PAL^ON^ OEOGY. 



and as wide or a little wider than long, strongly convex, some specimens 

 being higher or deeper than broad, most pi'ominent on the dorsal side 

 anteriorly, subtrigonal in a full edge view, and truncated in front. 



Ventral valve shallower than the dorsal, regularly convex in the 

 umbonal region and for about one half its length, but impressed anteriorly 

 with a rather short mesial sinus which is bounded on each side by a short 

 subangular ridge. At the front margin of this valve the mesial portion 

 is prolonged and bent abruptly inward, and the lateral portions are 

 minutely serrate or denticulate, there being apparently three minute 

 denticles on each side of the sinus. Beak of the ventral prominent, acute, 

 and but slightly incurved, the deltidium apparently longer (or higher) 

 than wide. 



Dorsal valve faintly plicated in the median line anteriorly, the fold 

 being longitudinally depressed in the middle and bounded on each side 

 by a short subangular longitudinal groove, which widens outward and is 

 followed by a short subangular lateral plication. 



In addition to the coarser markings already described, the surface is 

 •ornamented with fine lines of growth which are too small to be visible 

 without the aid of a lens. Over most of the surface, they are compara- 

 tively few and distant, but close to the anterior margin they are very 

 numerous and densely crowded. 



a. h. c. 



Fig. 3. Pugnax Kcrnahani. a, Dorsal view, — h, edge view, — and c, 



front view, of an adult specimen, in outline and of 



twice ttie natural size. 



Characters of the interior of the valves unknown. 



Dimensions of the largest specimen known to the writer : maximum 

 length 6-5 mm.; greatest breath, 54 mm.; maximum height or depth, 

 61 mm. 



A few specimens of this small and evidently very distinct ribless species 

 have recently been collected at Thedford by Mr. Kernahan and Mr. 

 Macintosh, who have kindly presented three to the Museum of the Survey, 

 and by Mr. Schucliert. 



Cyclokhina nobilis. Hall. 



Rhtimhospira nohilis, Hall. 1800. Thirteenth Rep. N. York St. Cab. Nat. Hist., p. 83. 

 Trenuitospira f mibilix. Hall. ISIiJ. Pal. N. York, vol. IV., p. 412, pi. 63, figs. 33—36. 

 liei-Jd [Trenialohpirii ) HohiUs, Whiteaves. 1S87. This volume, (advance sheets), p. 116. 

 Ci/otorAjna 7io6i7is. Hall and Clarke. 1893. Pal. N. York., vol. VIII, pt. 2, p. 207, pi. 

 61, figs. 1-12. 



