270 



Found ''in the Hamilton shales, at Hamburg-on-the-Lake, 

 Erie County, N. Y." (Hall, type.) 



Genus MODIELLA. Hall. 



[Ety. : Modus, a measure ; elliis, diminutive, dimin. of genus Modiola.] 

 (1870 : Pal. K Y., Vol. Y., Pt. I., p. 54.) 



Shells with equal, very inequilateral, valves, obovate in 

 outline. Anterior end short, ])Osterior broad and curved, or 

 obliquely sub-truncate, at the extremity. Anterior beaks 

 and arcuate cardinal line; hinge with elongate groove and 

 fold; linear ligament; fine concentric striae, and faint, curv- 

 ing, radiating striae, — are characteristic of this genus. 



MoDiELLA PYGMJEA. (Courad.) (Fig, 193.) (Pal. N, Y., 

 Vol. v., Pt. I., p, 514, PL LXXYl.) 



Bistinguishin<>- Characters. — Small size; obliquely obovate 

 outline, resembling Modiola; broadly curved to obliquely 



truncate posterior 

 margin; auriculate 

 anterior mai'gin, the 

 ear defined by a dis- 

 tinct sulcus ; curved 



Fig. 193. Modiella pi/gmcea. Two left valves, en- I'^tUt^tnig Stl UP. 

 largecl to two diameters (from Hall). FoUud tweutV-fivC 



feet below the Encrinal limestone, in Idlewood Ravine (very 

 rare) ; also in the Strophalosia bed on the Lake Shore (rare). 



Class Gastropoda. Cuvier. 



The gastropods, or snails, are molluscs, with a distinct head, a mus- 

 cular foot, and a mantle consisting of a single lobe. They are terrestrial, 

 marine, or fresh-water animals, and are commonly protected by a conical 

 or spirally-coiled shell, which is secreted by the mantle. The apical 

 portion of the shell usually consists of a simple coiled embryonic shell, 

 or protoconch. Succeeding this is the shell proper, which, when coiled, 

 comprises few or many whorls, the latter overlapping the earlier ones to a 

 greater or less extent. The suture at the junction of the overlapping 

 whorls may be faintly or strongly impressed. The whorls may coil 

 closely, forming a compact central columella; or they may be loosely 

 coiled, leaving a hollow columella, opening below in the umbilicus. The 

 body-whorl opens in the aperture, the rim or 2)eristome of which consists 



