OLENELLUS AND OTHER GENERA OF IMESONACID^ 235 



University of Lnnd, Sweden, sent me casts and specimens of the 

 species described by him. Dr. B. N. Peach most kindly guided me 

 to the Loch Maree locahties in northwest Scotland and, by the per- 

 mission of the Director of the Geological Survey of Great Britain, 

 Dr. J. Home, in charge of the Scottish Survey, sent me the material 

 in the collections of the Geological Survey and the Royal Scottish 

 Museum at Edinburgh. Mr. Frank Raw of the University of Birm- 

 ingham sent me photographs and plaster casts of the specimfens de- 

 scribed by him from the Comley sandstone of Shropshire, England. 



Dr. John M. Clarke, of the New York State Survey, loaned me 

 the Ford specimens of EUiptocephala asaphoides, and Prof. George 

 H. Perkins, State Geologist of Vermont, sent me the material in 

 the State Survey collections from western Vermont. The Director 

 of the Geological Survey of Canada kindly loaned the specimens 

 in the Survey Museum. 



Among the collectors who have assisted in obtaining the material 

 studied I wish to mention Mr. William P. Rust, of Trenton Falls, 

 New York, and Dr. Cooper Curtice, of Moravia, New York, both of 

 whom worked in the town of Georgia, Vermont, and in Washington 

 County, New York. Also Mr. F. B. Weeks, Mr. Henry Dickhaut, 

 and Mr. T. E. Williard, of the U. S. Geological Survey. 



The material of value from Alberta and British Columbia was 

 principally collected by Mrs. Walcott and myself during the summer 

 of 1909. 



To all I return my sincere thanks, and if I have omitted to men- 

 tion any who may have given assistance T trust that they will accept 

 an apolog}^ for my unintentional neglect. 



Order OPISTHOPARIA Beecher 



Order Opisthoparia Beecher, 1897, American Journ. Sci., 4th sen, Vol. 3, 

 p. 187. (Defined as below.) 



"Free cheeks general!}^ separate [but not in the Mesonacidre], 

 always bearing the genal angles. Facial sutures [when not in a 

 state of synthesis] extending forwards from the posterior part of 

 the cephalon within the genal angles, and cutting the anterior margin 

 separately, or rarely uniting in front of the glabella. Compound, 

 paired holochroal [ ?] eyes on free cheeks [or corresponding portion 

 of cephalon], and well developed in all but the most primitive 

 family." 



The words enclosed in brackets I have added to Dr. Beecher's 

 definition of the order. 



