34 CANADIAN FOSSILS. 



by fine transverse striae." Septa close (Hall), very flat. Siphunt,Io 

 small, its own diameter distant from the outer or ventral* border. 



Of this elegant species only two examples have as yet occurred, 

 both of which are figured. 



Locality. — Allumette Islands. C. annulatum, Hall, is more rare. 

 Orthoceras arcuoliratum, O. bilineatum, and O. laqueatum, are also found, 

 the first very common indeed ; and the Gonioceras anceps of the 

 Black-river limestone occurs with these. (See Preface.) 



Ctenodonta, Salter. 



Ctenodonta, Salter, 1851. Mollusca Lamellibranchiata. Family, 

 Arcacidae. Nearly equilateral, generally transverse, anterior 

 side largest ; beaks, approximate, not prominent ; hinge-line 

 with a double series of bent teeth, connected by smaller ones 

 beneath the beak ; ligament posterior, external, on a fulcrum : 

 no striated area or cartilage pit ; muscular impressions strong 

 (with supplementary scars), not bounded by elevated ridges; 

 pallial line simple. 



I was not aware, when I proposed the above generic term for a group 

 of palaeozoic Nuculaef , that the principal species had been previously 

 published under the name of Tellinomya by Prof. Hall. His recent 

 descriptions^ shew this to have been the case, and if the name did 

 not convey an entirely erroneous view of the affinities, I should have 

 been glad to restore it. But the chief characters of the genus reside 

 in the hinge and teeth, which are neither figured nor described by 

 him, casts only of the interior and the external surface having been 

 given in the plates of his excellent work, nor was the external 

 ligament observed. 



Mr. S. P. Woodward, in his most able treatise on the Mollusca, has 

 included my proposed genus under Isoarca of Munster, a group of 

 nuculoid shells which have the peculiarity of Ctenodonta so far as the 

 external ligament is concerned. But in Isoarca there is a ligamental 

 area, as in Area and Cucullcca, and the tumid beaks are remote, 



* The outer margin is often called dorsal, but there is an objection to using terms in 

 direct contradiction to the anatomical structure. 



t Reports British Association, 1851. Trans. Sect., p. 63. 



t Descriptions of New Palaeozoic Fossils ; extracted from the Reports of the Regents 

 of the University, Albany, 1856, p. 142. 



