NEW BRACHIOPODS OF THE GENUS SPIRIFER FEOM 

 THE SILURIAN OF MAINE. 



By Henry Shaler Williams, 

 Of Cornell Umvcrsity, Itliaca, 'New York. 



The species described in the following paper are particularly inter- 

 esting because of the relations they bear to well-lmown Silurian forms 

 while retaining a distinctive distribution of their specific characters 

 not heretofore observed. 



The fauna with which they are associated indicates a closer rela- 

 tionship to the Wenlock-Ludlow formations of Great Britain than 

 to the Niagara of the interior of the American Continent. 



Their source is the Edmunds formation of Washington County, 

 Maine. 



SPIRIFER <?DELTHYRIS) TRESCOTTI Williams. 



Plate 1, figs. 1-9, 11, 20, 22-23, 25. 



1828, cf. DeJthyris elevata Dalman Vet. Acad. Handlingar fur 1827, p. 120, 



pi. 3, fig. 3. 

 1867, cf. Spirifera elevata Dalman, Davidson, British Silurian Brachiopoda, 



pt. 7, No. 2, p. 95, pi. 10, figs. 8, 9, and 11. 



In external appearance the adult shells of this species resemble 

 Davidson's figures of " Spirifera elevata Dalman " shown on his plate 

 10, figures 8, 9, and 11 in British Silurian Brachiopoda. 



It is necessary to examine critically his definition in order to dis- 

 cover the points of difference. The following portions of Davidson's 

 description of " Spirifera elevata Dalman " may be used as they were 

 written in defining the form here under consideration : 



Transversely rhomboidal, hinge line nearly ( (a) ) as long as the 



width of the shell, cardinal angles ( (&) ) rounded. Dorsal valve less 



convex than the opposite one with ( (e) ) simple ribs, which are divided 



by a mesialfold, equaling in width the adjoining two ribs, moderately elevated 

 and grooved along the middle. Ventral valve much arched and gibbous ; beak 

 incurved ; mesial sinus as wide as the fold of the opposite valve and margined 



by- a strong rounded rib or ridge on each side; four ribs on either 



side of the sinus. Surface of both valves regiilarly crossed by numerous .slightly 



Proceedings U. S. National Museum, Vol. 51— No. 2144. 



78 



