134 CARBONIFEROUS LAMELLIBRANCHIATA. 



end very short and compressed, and forming a narrow lobe in front of the 

 gibbose remainder of the valve. The anterior border is convex above, but 

 becomes concave below. The inferior border almost circularly rounded, the 

 posterior obliquely truncate and almost straight. The hinge-line straight, of only 

 moderate length. The umbones are small, gibbose, slightly elevated, and placed 

 at the junction of the anterior and middle thirds of the hinge-line. 



Interior. — The anterior adductor muscle-scar is large and placed only a very 

 little distance within the antero-superior angle, oval in form. The hinge-plate 

 leaves a simple elongate groove in casts. 



Exterior. — The surface is ornamented with concentric lines and bands of 

 growth, with occasional, obscure, moderately broad, concentric sulci. Shell thin. 



Dimension*. — Plate XXV, fig. 8, measures — 



Antero-posteriorly . . . 47 mm. 



Dorso-ventrally .... 42 mm. 



From side to side ... 26 mm. 



Locality. — The upper beds of the Carboniferous Limestone, Kniveton, Derby- 

 shire. 



Observations. — Two specimens of this species have been obtained from Kniveton 

 Quarry, one (Plate XXV, fig. 8) having the left valve complete in front, and the 

 right posteriorly, the valves having slipped over each other. By studying both 

 valves, the real shape and character of each can be ascertained. The second shell 

 has also had the valves dislocated, and it is incomplete in front. 



The large anterior adductor scar and the elongate groove of the hinge-plate are 

 seen in the left and right valves respectively (Plate XXV, figs. 8, 8 a). 



Posidoniella sulcata, sp. nov. Plate XXV, figs. 2 — G. 



Specific Characters. — Shell of medium size, ovately subquadrate, moderately 

 convex with a small flattened posterior, superior angle. Margin ovately rounded 

 with a continuous pyriform curve from the anterior end of the hinge-line to the 

 postero-superior angle, which is slightly obtuse. Hingedine short and straight, not 

 produced forwards. The umbones are pointed, moderately convex and placed so 

 far forwards as to appear terminal. The anterior end is obsolete, its border 

 adpressed so that the valve is most convex at this point. There is no projection or 

 car in front of the umbo. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with numerous well-marked concentric 



