442 A. W. GRABAU THE SHERBURNE SANDSTONE 



18. Liorhynchus mesicosialw Hall 



This species also occairs in the Devonic of the Ural Moinitaiiis 

 of Eussia, but has not been reported from western America. It 

 is characteristic of the Chemmig and has also been observed in the 

 eastern ^^Sherbiirne." This form, as Hall says, may readily be 

 derived from L. quadricosta and L. muUicosta of the Hamilton by 

 suppression of the lateral plications. Variations within the Ham- 

 ilton species not infrequently lead to such obsolescence. The 

 specimens from the eastern Sherburne may thus be independently 

 derived. 



26. Pugnax pugnus (Martin) 



This is clearly an invader from the western fauna which char- 

 acterized the Dakota Sea. Its appearance in the upper part of the 

 Sherburne is remarkable. It occurs again 240 and 400 feet above 

 this formation in the Ithaca. Its latest invasion seems to be with 

 the High Point fauna. 



SI. ReticuJaria Icevis Hall 



This, the most characteristic species of the western Sherburne, 

 is a derivative from the Hamilton species, R. fimhriata. As shown 

 by H. S. Williams, ^° some specimens of R. la' vis still show the 

 fimbriated plicas near the anterior margin. The process seems to 

 have been one of retardation, the plicae appearing later and later, 

 until in most cases they did not appear at all. 



36. Stropheodonta mucronata Hall 



This species appears to be a direct derivative of S. perplana of 

 the Hamilton group. The variety tuUiiis of the Tully limestone 

 is, according to H. S. AYilliams, an intermediate form between 

 the two. 



Pelecypoda 



39. Actinopteria perstrialis Hall 



40. Actinopteria tenuistriata Hall 



Two small species derivable from Hamilton ancestors. 

 43. Aviculopeden lautus var. itliaccends Kindle 



Derived without doubt from the Hamilton species A. lautus. 



23 H. S. Williams: The life history of Bpirifer Uevis. New York Academy of Sciences 

 Annals, vol. ii, no. 6, 1882, pp. 140-160. 



