SOME NEW DEVONIC FOSSILS 233 



Nuculana (Ditichia) securis nov. 



Cf. Nuculana securiformis Goldfuss (sp.) Petrefacta Ger- 

 maniae. 2: 151, pi. 124, fig. 8 and Beushausen, Devon. Aviculiden 

 Deutschlands, p. 59, pi. 4, fig. 26-28 



Shell small, transversely elongated and snouted, beak approxi- 

 mately median, hinge line sloping slightly in front, deeply incurved 

 behind. Posterior extensions narrow, curved gently upward at the 

 extremity, anterior extremity broad and blunt ; umbones not promi- 

 nent, 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 extremity ; 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 



Nuculana (Ditichia) securis 



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 Sandberger 

 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 Nucu- 

 lana securiformis Goldfuss of the Coblentzian. 



The surface of the valves is covered with very fine concentric 

 striae. 



Lower Devonic. Dalhousie, N. B. 



