270 



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

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



Genus MODIELLA. Hall. 



[Ety. : .Von Jus, a measure ; ellus, diminutive, ditnin. of genus Modiola.] 

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



• 



Shells with equal, very inequilateral, valves, obovate in 

 outline. Anterior end short, posterior 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 PYGMiEA. (Conrad.) (Fig. 193.) (Pal. N. Y., 

 Vol. V., Pt, I.. i>. 514, PI. LXXVI.) 



Distinguishing Characters.— Small size; obliquely obovate 

 outline, resembling Modiola; broadly curved to obliquely 



truncate posterior 

 margin ; a u r i c u 1 a t e 

 anterior margin, the 

 ear defined by a dis- 

 tinct sulcus ; curved 



Fig. 103. Modiella pygmcea. Two left valves, en- radiating Stria?. 

 larged to two diameters (from Hall). Foillld tweiltv-five 



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 peristome of which consists 



