I. 



The Story of Olenellus. 



THE trilobite Olenellus, after forty years of comparative seclusion, 

 has of late attracted the attention of geologists to a degree 

 almost unprecedented among invertebrate forms of life. It has given 

 its name to a " zone " which, accepted though it is by Messrs. J. E. 

 Marr and H. B. Woodward, seems none the less of vast proportions 

 when compared with our ordinary conceptions of fossil zones ; it 

 takes the first rank in a fauna that includes 150 species of other 

 genera ; and it now absorbs our thoughts when we behold miles of 

 apparently unfossiliferous strata, or when we examine, for the 

 hundredth time, obscure organic markings treasured in cur own 

 collections. At the outset this unassuming creature bore other names 

 than Olenellus ; it was regarded as a family-dependent rather than as 

 an ancestor ; but in due time field-observation has raised it to the 

 most honourable position. 



When Dr. Ebenezer Emmons, in 1844 (i, p. 21), figured a flat- 

 tened and imperfect trilobite, and named it Elliptocephala asaphoides, 

 from the elliptical marking formed by the eyes and a part of the 

 glabella, he could not have foreseen the wealth of literature to which 

 his discovery would give rise. In fact, Elliptocephala and Atops were 

 the first two forms described from the now famous Olenellus-fauna, 

 and the historic site of their discovery has been fixed with precision 

 as near Reynold's Inn, west of North Greenwich, Washington 

 County, New York State (19, p. 638). Atops as a genus has dis- 

 appeared, and Elliptocephala was speedily absorbed into Olenus (Hall, 

 2, p. 256) ; but its lustre was only temporarily dimmed. After 

 describing Olenus thompsoni and Olenus vermontana, from the shales of 

 the Hudson River series at Georgia, Vermont (4, p. 60), James Hall 

 published a revised figure of the former, accompanied by a restora- 

 tion, and redescribed the species as the type of a new genus, Barrandia 

 (5, p. 115). The species vermontana became also included in this 

 genus ; but its full beauty was unknown till later, earth-stresses^ 

 having harshly dealt with the original, curtailing it of 19 segments. 

 Barrandia was thus defined as possessing only 13 or 14 thoracic 

 segments ; but the great development of the third segment was rightly 

 made a character distinguishing it from Olenus. Curiously enough, 

 this feature is shown in Emmons's original figure of Elliptocephala 



