368 A. W. GRABAU — SILURO-DBVONIC CONTACT IN NEW YORK 



This characteristic Manlius limestone species is quite common in the 

 Bullhead limestone of North Buffalo and Akron. The individuals are 

 of the size of the specimens figured by Vanuxem and Hall and agree 

 closely with them in form and proportions. 



The shell is ventricose, elongately ovoid to subpentagonal in outline, 

 most bulging in the posterior third. The beak of the brachial valve is 

 slightly incurved and overarched by that of the pedicle valve, which is 

 considerably more elevated. The mesial sinus of the pedicle valve is well 

 developed, narrow and prominent near the front; that of the brachial 

 valve is less prominent, being more of the nature of a flattening near 

 the anterior margin. The concentric lines of growth are very fine and 

 occasionally interrupted by strong wrinkles. Near the front of the 

 pedicle valve in mature or senile individuals an abrupt change of growth 

 occurs, the relative size of the valve becoming progressively reduced with 

 further growth. On this portion of the shell the lines of growth are more 

 prominent. 



This shell is readily recognized by its elongate character, strong ven- 

 tricosity, and well marked sharp mesial sinus in the pedicle valve. It 

 is not uncommon in the more compact portions of the rock, but in the 

 porous portions it appears usually as hollow molds. 



The measurements of an average pedicle valve are : Length, 9.5 milli- 

 meters ; width, 7.5 millimeters; convexity, 3.5 millimeters. 



WHITFIELDELLA CF. ROTUNDATA {WHITFIELD) 



(Plate 22, figures 3a-6.) 



Compare Nucleospira rotundaJta Whitfield. Annals of the New York Academy of 

 Sciences, volume ii, 1882, page 194, and Geological Survey of ( )hio, 1893, volume 

 vii, page 413, plate I, figures 11-14. 



Shell small, subcircular in outline, with the valves moderated con- 

 vex ; pedicle valve more strongly convex than brachial, slightly longer 

 than wide, with a pointed, gentty incurved, and slightly overhanging 

 beak. The greatest convexity of the valve is a little posterior of the 

 center, from which point the contour descends toward the beak, at first 

 with a gentle, then with a more abrupt curvature. The final portion of 

 the curve of the beak is approximately at right angles to the plane of 

 contact between the valves. Anteriorly the slope is a uniform curve. 

 A faint medial flattening or depression occasionally occurs ; rostral 

 cavity deep ; teeth supported by short, strongly diverging dental lamel- 

 lae, which appear to lie just beneath the cardinal slopes ; surface 

 marked by numerous lines of growth and by frequent (in some speci- 

 mens) stronger concentric wrinkles; brachial valve less convex than 



