EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 24 I 



is also a set of minute concentric striae, between thirty and forty in tlie width of one 

 line. 



The following are the dimensions of several specimens in lines, the first number 

 indicating the width of the hinge line, and the second the length. 16 — 12, 12 — 8, 10 — 6. 

 II — 7, 12 — 8, 14 — 10. 



This species differs from all others of the genus, yet discovered in Canada, by having 

 the ventral valve concave instead of convex. 



Locality and formation. In the Gasi)e sandstone at Gaspe, and in the limestone at 

 Split Rock, Perce. Lower Devonian. 



While this shell in its variations in outline from transverse to some- 

 what elongate, degree of echination, the occasional presence of a low 

 median fold on the ventral valve and other radial sinuosities, agrees with 

 the C h. CO mp Ian at a of the calcareous Oriskany of New York, yet our 

 specimens show that the striation of the surface is finer and apparently 

 uniform in most cases. Some of our casts show alternation or fasciculation 

 about the margins of the valves, but even in such cases less pronounced 

 than in C h. c o m p 1 a n a t a. There is also a less degree of reversed con- 

 vexity in the sandstone specimens which have been subjected to but little 

 compression, and further, in but few are the muscular markings so well 

 shown as on that species. All of these features serve to clothe the species 

 with distinction though we must admit the distinction is rather refined and 

 the two shells most closely related. In the character of its striation the shell 

 approaches the C h. h el d e r b e rg i ae Hall and Clarke, from the Helder- 

 bergian (New Scotland beds) of New York, and its relation to the C h. 

 complanata of Grand Greve is much the same as that of C h. 

 helderbergiae to the Ch. complanata of New York. 



The shells vary a good deal in size, an average specimen having a 

 length of 1 8 mm and a width along the hinge of 26 mm. Large examples 

 measure 30 by 45 mm, surpassing the dimensions of the large forms of 

 C h. complanata found in the Oriskany sandstone of Union Springs, 

 N. Y. 



Locality. Rather common in the sandstones, on the Portage road 3 

 miles west of Gaspe Basin and loose on the east side of the Southwest Arm. 

 We regard the specimens which Billings referred to as occuring at Perce, 

 as belonging to the species, C h. c o m p 1 a n a t a. 



Chonostrophia complanata Hall 



See Grande Greve fauna, p. 210 



Rare at the Portage road. 



