360 PALEONTOLOGY OF NEW YORK. 



tion. These are more or less irregular or sinuous, elevated at the concentric 

 varices and crossed by faint concentric lines. 



The typical example has a length of 21 mm. and a width on the hinge of 

 24 mm. 



Niagara group. Louisville, Kentucky. 



Plectambonites pbodccta, sp. nov. 



PLATE T.TYTTV, FIQS. 2S, 24, 25. 



The original of this species is an internal cast of the pedicle-valve, with 

 short, straight hinge ; rather narrow, depressed umbo, the shell becoming highly 

 convex and greatly produced anteriorly. The sides of the valve are somewhat 

 appressed medially and the anterior margin slightly expanded and suboval in 

 outline. The cast shows the impression of short, divergent dental plates and a 

 moderately broad muscular impression. The width of the shell on the hinge is 

 10 mm.; its length, 23 mm.; its convexity from the posterior margin, 8 ram.; 

 from the anterior margin, 28 mm. 



Niagara dolomites. Yellow Springs, Ohio. 



Spibifer cbispatus, sp. nov. 



PLATE XXXVI, FIGS. 9, 10. 



Shell small, with moderately high, incurved area, scarcely extended on the 

 hinge ; well-developed median fold and sinus, and three coarse plications on 

 each lateral slope. The surface is covered by conspicuous concentric lamellae. 



Niagara group. Maryland. 



Spirifer Canandaigu.*!, sp. nov. 



PLATE XXXVn, FIGS. 23, 84, 25. 



Shells of rather small size, having somewhat the aspect of an elongate and 

 umbonate &. Jimbnatus. Umbo of pedicle- valve prominent, narrow and closely 

 incurved at the apex. Hinge-line quite short, cardinal area small, incurved. 

 Median sinus deep, produced on the anterior margin, its anterior width being 



