218 PALAEONTOLOGY OF NEW YORK. 



The figures of Leptama Barabuensis, given by Whitfield, represent internal 

 casts of both valves indicating the existence of a supported spondylium in 

 each* It may be that Billings' Orihis ? Armanda,j from the Quebec group, 

 is an allied species with a radially striated exterior. 



The relations of these shells to Stricklandia = Stricklandinia are not 

 remote in these points of structure, and it may be inferred that they represent 

 the inception of the structure which is exhibited by the Stricklandinias of the 

 later Silurian and the Devonian. In the contour of the exterior a slight varia- 

 tion is presented by the Tripksia primordialis, Whitfield, :j: from the Potsdam 

 sandstone of Adams county, Wisconsin, and the Camarella calcifera, Billings, 

 from the Quebec group. ^ By the greater development of the median fold and 

 sinus the form of the shell becomes subtrihedral and resembles, not a little, 

 some of the Trenton limestone species of Triplegia ; but Camarella calcifera 

 possesses a very small spondylium in the pedicle-valve and probably one in the 

 brachial valve also. At present there seems no valid reason for excluding 

 these shells from the genus Syntrophia. They evidently bear no relation to 

 Triplegia. 



* Geology of Wisconsin, vol. iv, pi. i, figs. 6, 7 ; pi. iii, fig. 6. 

 t Paleozoic Fo.ssils, vol. i, p. 303, figs, a, b, c. 

 I Geology of Wisconsin, vol. iv, p. 172, pi. x, figs. 1, 2. 18S2. 

 § Canadian Naturalist and Geologist, vol. vi, p. 318. ISBl. 



