EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA IJl 



Uncinulus mutabilis Hall 



Plate 28, figures 3-8 



Rhynchonella mutabilis Hall. N. Y. State Cab. Nat. Hist, loth An. Rep't. 



1857. p. 66, fig. 1-3 

 Rh y n c h o n e 1 1 a 111 u t ab i 1 i s Hall. Palaeontology of New York. 1859. 3:225, 



pi. 29, fig. 4; pi. 30, fig. I, 2 

 Uncinulus mutabilis Hall & Clarke. Palaeontology of New York. 1894. 



V. 8, pt 2, p. 199, pi. 58, fig. 22-25 



With this species we identify provisionally a subspherical shell, which 

 apparently agrees in all respects with typical forms from the Helderbergian 

 of New York. These have shallow ventral and highly concave dorsal 

 valves, low flat or depressed plications with narrow interspaces, the number 

 of the plications varying considerably, but generally from 20 to 28, usually 

 simple, occasionally bifurcating, those on fold and sinus being 4-6. The 

 characters of the genus are well defined, the abruptly upturned margins of 

 the ventral valve, the sharply interlocking ribs along the commissures and 

 the fine zigzag concentric striation on the ribs about the margin, not inter- 

 rupted by a median line and the highly developed elevated cardinal plate 

 and bifurcate, grooved cardinal process. This is the most abundant of the 

 Rhynchonellas we have observed in the fauna. 



Locality. On the shore at Grande Greve. 



Plethorhyncha barrandii Hall 



Plair 28, figures i6, 17 



Rhynchonella b a r r a n d e i Hall. N. Y. State Cab. Nat. Hist. loth An. Rep't. 



1857. p. 82, fig. 1-3; p. 84, fig. 4 

 Rhynchonella barrandei Hall. Palaeontology of New York. 1859. 3:442, 



pi. 103, fig. 3-8 

 Plethorhyncha barrandei Hall & Clarke. Palaeontology of New York. 



1894. V. 8, pt 2, p. 191 



This shell characterized by the large size and sharp, strong, usually 

 simple and in respect to its associates, sparse plications, is represented in 

 our collections from Gaspe by a single well defined ventral valve from 

 Grande Greve. 



Plethorhyncha pliopleura (Conrad) 



Plate 28, figures lo-i"; 



Atrypa pleiopleura Conrad. N. Y. Geol. Sur. 5th An. Rep't. 1841. p. 55 

 Rhynchonella pleiopleura Hall. Palaeontology of New York. 1859. 



3:440, pi. 102, fig. 3, 4 

 Plethorhyncha pliopleura Hall & Clarke. Palaeontology of New York. 



1894. V. 8, pt 2, p. 191 



The large Oriskany Rhynchonellas which are of the type of Pletho- 

 rhyncha vary greatly in exterior expression on account of different degrees 



