436 Silurian and Devonian Fossils of Canada. 



bones about balf way to the posterior extremity of the hino-e line • 

 anterior, ventral, posterior and posterior half of dorsal margins 

 broadly and regularly rounded ; surface smooth, with a few short 

 stout spines. 



The specimen figured shews the anterior teeth : they are three 

 in number, and do not differ from those of C. rugosa, Length 

 eight lines; breadth the same. 



Locality and formation. — Pauqnettes Rapids, and Fourth Chute 

 of Bonne-chere, associated with fossils of the Trenton and Black 

 River Formations ► 



Collectors— Sir W. E. Logan, J. Richardson, E Billings-, 



Cyrtodonta obtusa (Hall sp.) 



(Ambonychia obtusa, Hall, Paleontology of New York. Vol. 1, p. 167. 

 Plate 36 ; Figures 8a, 86.) 



Fig- 13. pi ff . 14. 



Figure 13. Left valve from Pauquette's Rapids. 

 " 14. Interior of same shewing the teeth. 



Description. — The following is Professor Hall's description : 

 "Obliquely ovate, short, gibbous ; umbones short, obtuse, scarce- 

 ly incurved or bending forwards ; shell somewhat compressed to- 

 wards the lower margin, convex on the centre and becoming in- 

 flated above ; anterior side obtuse, rounded, scarcely extending be- 

 yond the umbones ; posterior side compressed, scarcely alated ; 

 cardinal line straight, margin of shell curving from its posterior 

 extremity ; surface V 



"The specimens seen are casts, where the markings of the shell 

 are not preserved. This species is distinguished from the others 

 by its short, ovate form, as well as the shorter, very obtuse and 

 gibbous umbones. It departs somewhat from the typical forms of 

 the genus [Ambonychia) ; but it has nevertheless the essential 

 features, and cannot be referred to any other genus." (Pal. N. Y., 

 vol. 1, page 167.) 



