EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA T,J 



Nuculana (Ditichia) securis Clarke 



Plate 7, figures 4-9 



Cf. Xucu Ian a securiformis Goldfuss (sp.) Petrefacta Germaniae. 2:151,1)1.124, 



fig. 8 and Beushausen, Devon. Aviculiden Deutschlands, p. 59, pi. 4, fig. 26-28 

 Nuculana (Ditichia) securis Clarke. N. Y. State Mus. Bui. 107. 1907. p. 233 



Shell small, transversely elongated and snouted, beak approximately 

 median, hinge line sloping slightly in front, deeply incurved behind. Pos- 

 terior extensions narrow, curved gently upward at the extremity, anterior 

 extremity broad and blunt ; umbones not prominent, umbonal ridge obscure ; 

 greatest convexity of the valve anterior near the hinge ; surface generally 

 convex over the body of the shell, depressed toward the posterior extrem- 

 ity; hinge toothed almost to the extremity of the posterior extension, while 

 the marginal surface along the extension is excavated and slightly ridged. 

 Just within the position of the muscle scars which are usually faint are two 

 faint shell ridges or clavicles preserved as grooves on the sculpture casts. 

 Of these the anterior is the larger, both are broad and low, but the structure 

 is altogether unusual though not unexpected in this genus. This structure 

 is expressed in Nuculites by the strong development of an anterior ridge 

 and in such forms occasionally the two ridges appear as in the species N . 

 (Cucullella) e 1 1 i p t i c a Maurer of the Coblentzian for which Sand- 

 berger proposed the generic term Ditichia because of this structure. 

 Beushausen however considers this development of a second ridge of only 

 specific value and embraces such species within Cucullella. For the same 

 reason we may hold the present species within the genus Nuculana though 

 shells of this lediform type have not before shown such structures. The 

 presence of these muscular clavicles is the only apparent difference between 

 this shell and the Nuculana securiformis Goldfuss of the 

 Coblentzian. 



The surface of the valves is covered with very fine concentric striae. 



Horizon. No. 11. 



Conocardium incarceratum Clarke 



Plate 5, figures 1-5 



Conocardium incarceratum Clarke. X. Y. State Mus. Bui. 107. 1907. p. 235 



This species will be found a close ally of C . i n c e p t u m Hall, whose 

 form and surface characters as occurring in the Oriskany of Becraft moun- 

 tain I have already delineated in State Museum Memoir 3. The shell 

 sometimes attains a larger size than the New York species ; its form is 

 the same but its exterior differs in the following particulars. The ornament 

 is not so fine, the radial lines less numerous and the deep concentric lamellae 

 can be traced continuously across the shell while in C . i n c e p t u m they 



