A NOTABLE TRILOBITE FROM THE PERCE ROCK 



BY JOHN M. CLARKE 



The list of Lower Devonic species occurring in that spectac- 

 ular cliff L'isle percee or Perce rock, has been given by the writer 

 with some degree of fulness in his volume on the geology of 

 Gaspe (N. Y. State Mus. Memoir 9, part i, 1908). Among these 

 species several trilobites of interest have been described. These 

 accounts were based upon the collections made during several 

 seasons of diligent work, and subsequent search has not mate- 

 rially added to the census of the fauna. The past summer, how- 

 ever, brought to light two specimens of a commanding Homalo- 

 notus, a genus not hitherto recorded from any of the Devonic 

 outcrops in Gaspe county, and not only its presence but the char- 

 acter of the species itself is worthy of note. 



The Homalonoti of the boreal Paleozoic regions in America 

 are distinctively characterized by their freedom from dermal 

 overgrow'ths. They carry no spines or tubercles on any part of 

 the test. This is a statement subject of course to the limitations 

 of our pretty considerable knowledge of the Paleozoic faunas on 

 this continent and while applicable here, it can not be so broadly 

 stated for the boreal Palezoic, particularly Devonic, Homalonoti 

 of the eastern hemisphere. There are European species of which 

 the Siluric H. k n i g h t i and the Devonic H. armatus are 

 leading and almost sole examples, whose test is spiniferi)us or 

 tubercied, while the predominant species are devoid of these 

 grow^ths as in America. 



The armate Homalonoti are on the whole quite distinctively 

 austral, especially in their Devonic distribution. Witness of this 

 is the great abundance of H. herscheli Murchison in the 

 South African Lower Devonic^ and at the same horizon in the 

 Falkland islands. 



There is an abundant and often beautifully preserved species 

 in the Lower Devonic shales of Sao Paulo, Brazil, termed by the 

 writer H. n o t i c u s, w^hich is free of spines save for one con- 

 spicuously developed on the epistoma, a structure which is pres- 

 ent in H. herscheli, but absent in all boreal species. 



1 The large number of species of this genus described by the writers on 

 the South African Devonic has seemed to me not justified by evidence, except 

 for provisional purposes. 



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