EARLY DEVOiNIC HISTORY OF NEW Y^ORK AND EASTERN NORTH AMERICA 1 99 



Orthothetes (Schuchertella) becraftensis Clarke 



cf. Ortli. arctostriata Hail 

 Plate ^i, figures i-& 



O r t li t h e t e s becraftensis Clarke. N. Y. State Mus. Mem. 3. 1900. p. 51, 



The species at Becraft mountain is quite uniformly of small size, with 

 rather coarse ribbing, the plications being simple and rounded, increasing 

 by hiiplantation and crossed by very fine concentric lines. Specimens of 

 this typical expression occur in the Grande Greve limestone but here it is 

 evident that the small size is not a universal feature and must be properly 

 estimated as a specific character of the local and typical development of the 

 shell. Gaspe specimens reach to larger proportions, on these the striae 

 becoming more numerous and relatively finer with age under which con- 

 dition the shell puts on the aspect of Orth. arctostriata. We there- 

 fore incline to the view that the New York O. becraftensis represents 

 a condition in which development did not progress beyond the characters 

 described for that species while in the fertile Gaspe basin it progressed to a 

 more advanced stage of development. 



..Localities. Not uncommon in the higfher beds on the Grande Greve 

 shore, in Dolbel's brook and at Indian Cove. 



. -Orthothetes (Schuchertella) woolworthanus Hall mut. gaspensis nov. 



Plate 41, figures 9-14 



;'■ 5^^ S t ro'p home n a w o o 1 w o r t h an a Hall. Palaeontology of New York. 1859. 

 • V. 3, p. 192, pi. 17, fig. I, 2; and Orthothetes woolworthanus Hall & 

 . . Clarke. Palaeontology of New York. 1892. v. 8, pt i, pl. ir, fig. 25-29, 31 



A>5 is well known it is not easy to discriminate species differentials in 

 members 'of the genus Orthothetes. .In the forms before us we are pre- 

 sented With a.' shell which approaches in general aspect O. w o o 1 w o r t h- 

 anus oi the' Helderbergian (New Scotland) shaly limestone; it has the 

 long and straight hinge, subsemicircular rarely subelliptical outline, some- 

 times elongated and in the character of the surface there is comparatively 

 little difference. We observe however that in O. av o o 1 w o r t hanu s the 

 ventral beak is rarely greatly elevated and distorted while this distortion is 

 present .in mut. gaspensis, giving the valve at times the aspect of O. 

 defdrmis Hall (New Scotland beds)v The shell substance is much the 

 thicker in the latter; the muscle scar of the ventral valve is much laro-er 

 in the mutation and the pallial surface is. vascular. In the dorsal valve the 

 muscle scar of the mutation is larger, sharply subdivided and the pallial 

 surface strongly marked with impressions of mantle vessels, the trunks of 

 wliich are median, departing forward from the front end of the muscle area. 



