Marylaxd Geological Survey 427 



The fauna of this zone also bears some resemblance to that found in the 

 higher beds containinsi' the lihaca fauna at Catawissa, Pennsylvania.' 

 This is shown by the presence of Pterinea cliemungensis and Edeno- 

 dcsma hirostratnm at botli localities. The latter species is confined to the 

 Liorliynclius glohnliforme zone in Maryland. 



Althoufiii many species of the Ithaca fauna occur in the Hamilton 

 formation, it is interesting to note that it contains many forms of dif- 

 ferent origin, including some of its more important members. Among 

 these are Spirifer mesastrialis, Productella speciosa, Liorhynchus glohuli- 

 formCj Pugnax jnignus var. alius, and Scldzoplwria striatula. While there 

 are Hamilton elements in the fauna, it cannot properly be called a recur- 

 rent Hamilton fauna in a strict sense and difi'ers greatly from the assem- 

 blage next to be descril)ed. 



Parkhead Sandstone Member. — Among the most important and 

 characteristic species of this member are: Trupidoleptus carinatus, Spiri- 

 fer (Delthyris) mesacostaUs, S. marcyi var. superstes, Camarotwcliia. 

 congregata var. parl-lieadensis, liliipidomella vanuxemi, Cyrtina liuiniJ- 

 tonensis, Cypricardella hellistriata, Liopteria higshyi, Coleolus teniiicinc- 

 tits, Cyclonemina multistriaia, and Pleurotomaria capillaria, all of which 

 occur in the Hamilton, save Cyclonemina multistriaia, a new species. 

 One of the most abundant species is Tropidolepttts carinatus, which is 

 the most characteristic member of the Hamilton fauna, according to 

 Williams, who terms that fauna the Tropidolc])tus carinatus fauna.' 



An examination of tlie table of distribution, in which all the species 

 of this member are listed, shows that the entire assemblage jiossesses a 

 pronounced Hamilton aspect, about 66 per cent of its species occurring in 

 the Hamilton formation of New York. That it is, however, later than the 

 Hamilton is shown by the modification of some of the species, as, for 

 example, Spirifer marcyi, which is present as a mutation, and also by the 

 presence of a considerable number of species of later age. The fauna is 

 manifestly a recurrent Hamilton fauna with an addition of later species. 



' Kindle and Williams. Bull. U. S. Geol. Survey, No. 244, p. 77, 1905. 

 ' Bull. U. S. Geol. Survey, No. 210. 1903. p. 50. 



