EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 205 



Closely allied to O. planoconvex a, Hall, Palaeontology of New York, volume 3, 

 plate 12, but differs in having no area as that species has. 



Locality and formation. Indian Cove, Gaspe, in limestone no. 8. 



Mr Billings very properly compared the species to O. planoconvexa 

 of the Helderbergian fauna which it resembles not alone in contour but in 

 the character of the mu.scle scars on both valves. The shell is of a form 

 unusual in the Devonic but highly characteristic of late Siluric stages. 



Dimensions. Average length 2 1 mm, width 2 1 mm. This species 

 occurs quite freely in the Oriskany of Glenerie in finely replaced specimens 

 and imperfect specimens from Becraft mountain doubtfully referred by the 

 writer to Dalmanella perelegans [N. Y. State Mus. Mem. 3, p. 57] 

 are evidently of the same character. Orthis discus of the Helder- 

 bergian is a close ally but has more equally convex valves. 



Locality. We have found this shell to be quite rare at localities about 

 Grande Greve. 



Chonetes canadensis Billings 



Plate 45, figures 16-27 



C h ne tes c a n a d en i s Billings. Palaeozoic Fossils. 1874. v. 2, pt i, p. 17, fig. 7 



Original description. Shell semicircular or semielliptical, the proportional length and 

 width variable. Ventral valve gently convex, in general most elevated at about one third 

 the length of the beak; the cardinal angles flattened or slightly concave; umbo broadly 

 depressed, convex; beak scarcely distinguishable from the cardinal edge. The area is 

 rather large, being about a line high at the beak; nearly flat or very slightly concave, 

 nearly smooth, no traces of crenulations; inclining backwards at an angle of about 45° 

 with the plane of the lateral margin. The foramen is triangular, its width at the base 

 nearly twice its hight, extending nearly to the beak. 



Dorsal valve gently concave, corresponding to the ventral valve, in its curvature, so 

 as to leave only a thin space between them. The area is about one third or one half the 

 size of that of the ventral valve, and forms nearly a right angle with the plane of the 

 lateral margin. 



The surface is covered with very fine, obscure radiating striae, from ten to fifteen 

 in the width of two lines. Some specimens, also, exhibit a number of concentric ridges 

 or undulations of growth. Many show shallow, concave furrows from half a line to one 

 line wide, which radiate from near the beak to the margin. These are most distinctly 

 seen in specimens from which the shell is either wholly or partially removed. In such 

 cases these furrows are either straight or slightly curved, the convex side of the curve 

 being outwards, towards the sides. When the shell is a little worn fine closely arranged 

 punctures may be seen between the striae. When the shell is removed, the cast of the 

 inner surface is sometimes quite rugose with punctures and obscure irregular tubercles. 

 Often, however, the cast only exhibits the radiating striae. 



In some specimens, the cardinal edge of the ventral valve is quite sharp, and does 

 not exhibit any indications of spines. In others there are four or five small tubercles or 

 rudimentary spines, on the cardinal edge. When they can be seen they appear to be 

 short, nearly erect or curving slightly inwards. The following are the dimensions of 

 several specimens in lines, the first number in each case being the width, 6 — 3;^; 16 — 

 10; 20 — 12; 22 — 12; 24 — 14. 



Small specimens of this species have nearly the proportion of C h. m e 1 o n i c a but 

 are always nearly flat, while those of the latter are always more convex. 



