46 NEW YORK STATE MUSEUM 



substance which so frequently characterizes this species under certain 

 conditions of weathering. 

 Horizon. Nos. i, 8, 9. 



Leptostrophia becki Hall 



See pt i, p. in 



Stropheodonta beckii Hall. Palaeontology of New York. 1859. 3:191, pi. 22, 

 fig. i a-t 



Specimens of this species in this fauna apparently agree fully with 

 those of the Helderbergian of New York. 

 Horizon. Nos. 8, 9, 1 1. 



Leptaenisca concava Hall 



Plate 10, figures 7-11 



L eptaena concava Hall. Palaeontology of New York. 1859. 3: 197, pi. 1 8, fig. 2 

 Leptaenisca concava Beecher. Am. Jour. Sci. 1890. 40:838, pi. 9, fig. 1-9 



Leptaenisca concava Hall & Clarke. Palaeontology of New York. 1894. v. 8, 

 pt 2, p. 300, pi. 15, fig. 30, 31; pi. isA, fig. 19-21 



When Beecher described the genus Leptaenisca there was but one 

 species known, the L. c o n cav a of the Helderbergian. We subsequently 

 described as additional species from the same fauna two smaller forms, L. 

 adnascens and L. tangens [op. eit. 1894] which then seemed to 

 differ from the larger both in form, surface sculpture and degree of attach- 

 ment or size of cicatrix. We have before us in the Dalhousie fauna shells 

 which at maturity present the characters of L. concava; their deeply 

 convex and concave shells, with a cicatrix well developed, the form arched 

 but frequently distorted in growth and some of these present a median flat- 

 tening or sinus pretty well denned on the earlier portions of the ventral 

 valves though this disappears in later growth. This median depression is 

 one of the differentials of the smaller species L. tangens and L. 

 adnascens and may indicate the possibility that the latter represent 

 miniature conditions of L. concava. The presence of Leptaenisca 

 concava in these beds is our first knowledge of the occurrence of the genus 

 outside of the early Devonic of New York. The species are rare members 

 of the Helderbergian fauna. At Dalhousie the shells are quite abundant. 



Horizon. No. i. 



Orthothetes (Schuchertella) radiatus Hall 



S t r o p h o m e n a radiata Hall. Palaeontology of New York. 1859. 3: 191, pi. 21, 

 fig. 8, 9 



The Helderbergian species appears to be present at Dalhousie in 

 normal development. 

 Horizon. No. n. 



