A NEW DEVONIAN BRACHIPOD— WILLIAMS. 269 



cle valve extends upward with onl}" slig-ht inward curvature directly 

 above the cardinal area, which lies nearly in the plane of the margin 

 of the shells, the tip of the beak slightly overarching- the pseudo-area. 

 The angle formed by the sides of the beak is from 120*^ to 140 . 



The surface ornamentation is made up of strong linear striie, of 

 which 45 to 75 can be counted, consisting of rounded thread-like 

 ridges separated by rounded grooves, giving the surface a striate 

 appearance somewhat coarser than that of normal R. ovoides. 



The musculature is strong in well-preserved specimens and corre- 

 sponds very closely to that of Beaehia auessana for both the pedicle 

 and brachial valves. The crural bases are two widely separated, strong, 

 round bars in the molds leaving two well-defined holes each side of 

 the base of the cardinal process. No evidence of the shape of the 

 brachial supports is present. The shell structure appears to be tibrous; 

 no puncta> have been discovered. The visceral foramen is indicated. 



The molds of the interior differ greatly, according to the age and 

 strengthening of the shell, especiall}^ the pedicle valve. In the 

 younger shells the dental lamellas are thin and separate two lateral 

 cavities from the central muscular cavity. The lateral cavities reach 

 nearly to the hinge margin. As the umbonal cavity of the shell 

 becomes tilled, by thickening of the shell substance, the central mus- 

 cular cavit}^ between the hinge plates is represented in the mold by a 

 rounded ridge bounded by the dental lamellte, the lateral cavities 

 being completeh^ filled by shell deposit. This rounded ridge, extending 

 beakward from the main mass of the internal tilling of the shell in the 

 molds, increases in width with the elevating of the pseudo-area. In 

 extreme examples the shell deposit is fully one-fourth inch in thick- 

 ness, thus giving to the interior markings of the shells great difference 

 of form, according to the age of the shell. 



Tyjje. — The two specimens figured are designated as cot^^pes of the 

 species. They are now in the collection of the U. S. Geological Survey, 

 with the other material on which the description is based, and will be 

 transferred to the U. S. National Museum. 



The species is al)undant in the shales and sandstones of the Chapman 

 formation of Presque Isle Brook and Edmunds Hill in Chapman Town- 

 ship, Aroostook County, Maine. 



