_■ >• I 



Leiorhynchus quadricostatum. (Vanuxera.) (Fig. 14-"..) 

 (Pal. X. Y., Vol. IV.. p. 357. PI. LVI. ) 



Distinguishing Characters — Broadly ovate outline : almost 

 smooth lateral slopes, the plications being very faint: small 



- 



Fig. 143. Leiorhynchus quadricostatum. Two brachial valves and one pedicle valve, 

 natural size, all much distorted <from Halli. 



number (three to five) of rounded plications on the fold and 

 sinus. This species is normal in the Genesee slate, but has 

 not been found in it in the region under discussion. Speci- 

 mens approaching- it in character, if not identical with it. 

 occur in the upper Moscow shale, at Section 1. 



Leiorhynchus limitare. (Yanuxem.) (Fig. 144. ) (Pal. 

 N. Y., Vol. IV., p. 356, PL LVI.) 



Distinguishing Characters.— Ovate to sub-orbicular out- 

 line; gibbous char- ^^ ^ 

 acter of old uncom- f^ LI < ^0^" 

 pressed speci m ens ; $v V. * 



mesial fold and sinUS Fig. 144. Leiorhynchus limitare. Dorsal, profile, and 



front views of a small specimen (from Hall). 



become developed 



near the front; numerous angular or sub-angular plications, 

 those of the fold and sinus bifurcating, those of the lateral 

 slopes rarely dividing; fine concentric stria?. 



Found in the lowest ten feet of the Transition shales, in 

 the Lake Shore sections; upper Marcellus shales, in Bay 

 View Cliff. 



Leiorhynchus dubium. Hall. (Fig. 145.) (Pal. X. Y.. 

 Vol. IV., p. 364, PL LVII.) 



Distinguishing Characters. — Ov ate outline, rapidly ex- 

 panding towards the front; moderate and almost equal 

 convexity of valves ; very faintly developed fold and sinus; 



