216 PALEONTOLOGY OF NEW YORK. 



Gknds SYNTROPHIA,* gen. nov. 



PLATE LXII. 



1861. Oamarella, Bilunos. Canadian Naturalist and Geologist, vol. vi, p. 818. 



1862. Strlcklandiniaf, Billings. Palieozoic Fossils, vol. i, p. 85, figs. 77, 78. 



1864. Oithis, A. Wi.nchkll. American Journal of Science, second series, vol. xxxvii, p. 229. 



1883. LeptCBna, Triplegia, Wiiitfibld. Geology of Wisconsin, vol iv, p. 171, pi. i, figs. 6, 7 ; pi. iii, fig. 6 ; 



p. 172, pi. X, figs. 1, 2. 

 1888. Triplesia, Whitfikld. Bull. American Mus. Nat. Hist., vol. i. No. 8, p. 303, pi. xxiv, figs. 9-11. 

 1892. Syntrophia, Hall. • Palaeontology of N. Y., vol. viii, part i, p. 270. 



In considering the spondylium-bearing shells of the earlier faunas, there are 

 great difficulties in the determination of positive taxonomic characters. The 

 features of the exterior and, to a great degree, those of the interior, are plastic 

 and variable, failing to assume that fixity of form possessed by their successors 

 in later faunas, and upon which we depend for a proper conception of generic 

 values. Here circumspection must be used, lest generic distinctions be too 

 arbitrary, or too narrowly drawn on the basis of differences which, among 

 later fossils, would properly be considered of higher significance. The earlier 

 divisions must be allowed more elasticity, as the types they include are forma- 

 tive and inconstant. The spondylium-bearing species of the Lower Silurian 

 are mostly subtrihedral shells with the external aspect of Rhynchonella, but 

 there are a few described species which have an exterior similar to members of 

 the genera Protorthis and Billingsella, that is, they are small, transversely 

 elongate in outline, with straight, well-defined cardinal area. Such are the 

 Stricklandinia ? Arachne and S. Areihtcsa, Billings, of the Quebec group (Lime- 

 stone No. 2) ; Orthis Barabuensis, A. Winchell, from the Potsdam sandstone of 

 Baraboo, Wisconsin, and the Triplesia lateralis, Whitfield, of the Calciferous 

 fauna of New York and Vermont. For these shells the name Syntrophia will 

 be adopted, the last-named species being selected as the type of the group, 

 since the material derived from various sources has afforded the means of 

 obtaining a very clear conception of its external and internal features. 



" The TVipUsia lateralis, Whitfield, of the Fort Cassin beds (Calciferous sandstone), contains a spoon-shaped 

 process in each valve, that in the pedicle-valve being supported by a median septum. It therefore becomes 

 necessary to remove this form to a distinct genus and to a diffei-ent association, and it will be described and 

 Ulostrated in its proper place under the name SYNTnormA." — Palseontology of New York, vol. viii, part i, 

 page 270. (This note was printed in 1891.) 



