2SJ8 ROYAL SOCIETY OF CANADA 



I hesitate to make them into new species as the evidence points rather 

 to a variable habit of growth of a common species. The t\^^o extreme 

 formfi, at least, may be identified as Dalmanella concinna and Schizo- 

 phoria muUistriata. In this series the subgeneric characters appear to 

 be of varietal value. 



7. Orthis (Rhipidomella) ohlata. Hall. 



A few specimens of slight convexity associated with the series by 

 their surface markings may be listed under the name Rhipidomella 

 oblata. They are of medium size and convexit}', one specimen showing 

 the oblate form, the width being greater than the length, others being 

 too imperfect to make outline certain. The surface lineations are fine 

 and there is no evidence of medium fold or sulcus on either valve, the 

 interior is not in evidence. Externally, there is little to distinguish 

 them from the species listed as Orthis subcarinata except the absence 

 of any subcarination along the median line of the pedicle valve. 



8. Orthis (Orthostrophia) strophomenoides, Hall. 



. Three specimens exhibiting the characteristic form and one of these 

 showing the muscular scar of the pedicle valve are in the collection. 



9. Leptœna rhomhoidalis^ Wilkens, 



This form is present in several specimens presenting the general 

 characters shown in Ilall's plate illustrating the Lower Helderberg 

 " Strophomena rugosa.'' 



10. Stropheodonta arata, Hall. 



Numerous specimens of this species are in the collection. The 

 ventral valves exhibit the gently arching umbonal portion of growth, 

 the rapid curvature or geniculation toward the front and the surface 

 lineations characteristic of this species, but the average size is larger 

 than the typical forms. They agree, as Schuchert i remarked, with the 

 Kew Scotland variety " Stropheodonta variastriaia var. arata, Hall as 

 found at Becraft Mountain near Hudson, New York." 



The largest St. Helen's specimen measures 27 by 35 mm., which is 

 intermediate in size between the typical specimens figured by Hall, and 

 those figured by Clarke from probably the same locality and described 

 by him under the name Braciiy prion major? Our smaller specimens 

 agree more closely with the typical Stropheodonta arata. From Clarke's 

 description and figureis it does not appear clear wherein his species is 

 to be distinguished from ^. arata. In the description of B. major the 

 " jiUform striœ alternating with a group of siihequal fine ones" is said 



1 Schuchert, C, On the Helderbergian Fossils near Montreal, Am. Geologist, 

 XXVI, 1901, p. 249. 



2 Clarlie, J. M., Oriskany fauna of Becraft Mountain, Columbia County, N.Y., 

 Mem.. No. 3, N. Y. State Mus , 1900, p. 54, PI. S, Figs. 8-13. 



