LOWER HELDERBERG ROCKS. 379 



which becomes less conspicuous on the ventral margin. Border some- 

 times scarcely marked on the ventral margin, and becoming wider 

 above and subalate on the hinge extremities : ventral edge abruptly 

 bent inwards with a distinct groove, which is wider in the centre and 

 is discontinued at the anterior and posterior margins, allowing its two 

 edges to come together, forming the thickened inner border which 

 marks that part of the shell. Beyond these the entire margin is in- 

 curved, slightly thickened and crenulate, with a neatly defined groove 

 just within it. 

 Surface finely punctate or striato-punctate. 



This species differs from the preceding in being proportionally shorter, and in 

 the greater prominence and inequality of the posterior lobe, as well as the lesser 

 prominence of the ventral margin and the smoother surface. 



Fig. 2 a. A specimen, natural size. 



Fig. 2 b. The same enlarged four diameters. 



Fig. 2 c. Another specimen, presenting some slight variations. 



Fig. 2 d. Profile showing the elevation of the central and lateral lobes. 



Fig. 2 «. Magnified view of the ventral margin and the ventral groove, with the outer 

 groove and crenulated edge. 



Geological position and locality. In the pentamerus limestone of the Lower Hel- 

 derberg group : Schoharie county. 



Beyiicliiii iiotata (n.s.). 



Plate LXXIX B. Fio. 3 a, b, c. 



Carapace semioval, moderately convex, the length about once and a half 

 the height, more or less symmetrical, the anterior end usually narrower 

 than the posterior; marked by two transverse furrows, which reach 

 about halfway from the dorsal to the ventral margin, the anterior one 

 faintly curving backwards at the base. Middle lobe short, broad oval, 

 reaching nearly halfway to the ventral edge : anterior lobe larger than 

 the posterior, flattened at the antero-dorsal extremity. Ventral side 

 gently incurved, bordered by a nearly flat rim which is straight in the 

 middle of the base, and visible along the entire outline from the dorsal 

 extremities : dorsal line straight. 



Surface finely granulose. 



