458 



GEOLOGY. 



basin and to have followed the Helderberg fauna into the interior as 

 a distinct invasion. 



Preponderance of large brachiopods. — More than half of all the known 

 species of the Oriskany fauna are brachiopods. 1 Their most obvious 

 feature was their great size. The Pentamerus oblongus (Fig. 187, o) 

 of the Silurian period and a few other previous forms had been large, 

 but at no time had there been a fauna made up of species from differ- 

 ent genera and even different families which attained such ample 



Fig. 207. — The Oriskany Fauna. Brachiopoda: a, Rensselceria ovoides (Eaton); a 

 representative of a genus restricted to the Helderbergian and Oriskany (see Fig. 

 206, (h); b, Hipparionyx proximus Van., one of the most characteristic fossils of 

 the arenaceous Oriskany beds; c, Camarotcechia barrandei (Hall), one of the large 

 rhynchonelloid shells of the Oriskany; d, Spirifer murchisoni Castel, and e, Spirifer 

 arenosus (Con.), two of the most characteristic Oriskany species, the first occurring 

 throughout the fauna, the second mainly in the fauna of the arenaceous beds; /, 

 Stropheodonta magnified Hall; a species which sometimes grew to be four or five 

 inches across. The genus has its great expansion in the Devonian. (Weller.) 



dimensions as those of the Oriskany. Spirifer arenosus (Fig. 207, e), 

 Rensselceria ovoides (Fig. 207, a), Stropheodonta magnifica (Fig. 207, /), 

 Hipparionyx proximus (Fig. 207, b), and Camarotoechia barrandi (Fig. 

 207, c), all reaching lengths or breadths of two and one-half to four 

 inches, made up an aldermanic group that seems all the more notable 

 for its sandy habitat, though sandiness at the bottom of the sea does 

 not imply sterility in the same sense as sandiness on the land. There 

 were small brachiopods associated with these giants, but they were 



1 Schuchert, Rept. N. Y. State Geologist for 1888, p. 51. 



