334 Annals of the Carnegie Museum. 



Family Ambonychid.e Miller. 



Genus Clionychia Ulrich. 



9. Clionychia montrealensis (Billings). (Plate XXIX, figures 18-24.) 



Vanuxemia monlrealetisis Billings, Canadian Naturalist and Geologist, Vol. IV, 



1859, p. 447, figs. 25, 26; Geology of Canada, 1863, p. 131, figs. 6ia ,6ib. 

 Clionychia montrealensis Whiteaves, Ottawa Naturalist, Vol. XXII, 1908, p. 107. 



Description. 



Shell of medium size, sub-triangular in outline, beaks terminal and 

 directed forward. Umbones narrow and depressed. The greatest 

 convexity of the shell is along the middle of the valve. The anterior 

 slope is somewhat more abrupt than the posterior, and the posterior 

 side is drawn out into a short wing. The posterior margin is gently 

 convex, and makes an angle of about 100° with the hinge. The basal 

 margin is nearly semicircular, and the anterior margin straight or 

 slightly concave. 



One specimen is 12 mm. long and 14 mm. high, and another 13.5 

 mm. long and 15 mm. high. 



Locality. — This is one of the commoner species in the middle and 

 Upper Chazy at Valcour Island and Chazy, New York, and Montreal, 

 Canada. The types are a small right valve and a larger left valve 

 on a small piece of limestone from Montreal. 



10. Clionychia marginalis Raymond. (Plate XXIX, figures 25, 26.) 



Clionychia marginalis R.a.ymond, American Journal of Science, (Ser. 4), Vol. XX. 

 1905. P- 373. 

 Most specimens of this species are larger than those of C. mon- 

 trealensis, and can readily be distinguished from that species by the 

 almost perpendicular front slope, the shorter hinge line and the less 

 oblique axis of the shell. 



Description. 



Both valves moderately convex, the umbones somewhat depressed, 

 but increasing rapidly in height, the greatest thickness of the valves 

 being at about one-third the distance from the beak to the lower 

 margin. Hinge line short. The posterior margin is broadly rounded, 

 the lower margin semicircular. The front is almost straight. The 

 greatest convexity is along a line parallel to the front. The posterior 



