26 bulletin: museum of comparative zoology. 



species, E. deltoideus Shumard and E. nereus Hall, have as many as 

 eight pairs of ribs. Most of the species have seven pairs, one, E. 

 americanus Vogdes, has six, and E. elegantulus Billings has only five. 

 The species may be taken up in alphabetical order. 



E. americanus Vogdes (Description new Crustacea from Clinton of 

 Georgia, 18G6, p. 1), has only six pairs of ribs on the pleura, and no 

 pustules, thus ruling it out at once. 



E. deltoideus Shumard (Geol. Missouri, 1855, p. 198, pi. B, f. 10), is 

 similar in many ways to E. reflexus, having the rings very numerous, 

 twenty-four in nvimber, and interrupted by a smooth lane. There 

 are, however, no pustules except very indistinct granules, on this lane, 

 and the ribs, of which there are eight pairs, are likewise smooth. 



E. egani S. A. Miller (Journ. Cine. soc. nat. hist., 1880, 2, p. 254, 

 pi. 15, f. 1, lb), has a long terminal spine, only seven pairs of ribs, 

 which are narrow with wide interspaces, and while the axial lobe of 

 the pygidium is on the same plan as in E. reflexus, it has fewer rings 

 and tubercles. 



E. elegajitulus Billings (Cat. Silurian fossils Anticosti, 1866, p. 62), 

 has only five pairs of ribs, the median lane on the axial lobe is without 

 tubercles, but the first eight rings cross it. 



E. indianaensis Kindle (28th Ann. rept. Dept. geol. and nat. res., 

 Indiana, 1904, p. 482, pi. 24, f. 14, 15), is a very peculiar species, not 

 at all of the same type as the one under discussion. It has fifteen 

 rings on the axial lobe and ten pairs of ribs. Each rib crosses the axial 

 lobe and has three to five tubercles. 



E. nereus Hall (20th Rept. N. Y. state cab. nat. hist., 1868, p. 375, 

 pi. 21, f. 15) has no flattened lane along the top of the axial lobe, and 

 no nodes on the rings or ribs. 



E. ornatus Hall and Whitfield (Pal. Ohio, 1875, 2, p. 154, pi. 6, f . 16) is 

 c^uite similar to the present species, but has only seven pairs of ribs, and 

 the ribs themselves are narrower and the spaces between them wider. 

 There are also only twenty rings and five nodes on the axial lobe. 



E. thresheri Foerste (Bull. Sci. lab. Denison univ. 1887, 2, p. 101, pi. 

 8, f. 26) is a small species which is similar to the last and to E. reflexus. 

 There are, however, only seven pairs of ribs, which are themselves 

 exceedingly narrow; there are also only eighteen rings on the axial 

 lobe, and six pustules on the smooth lane. 



E. tuber culifrons Weller (Bull. Chicago acad. sci.. 1907, no. 4, pt. 2, 

 p. 259, pi. 24, f. 12, 13) is a small form with a short wide pygidium 

 which is without nodes and the rings of which cross the axial lobe 

 without interruption. 



Formation and locality: — From the Niagaran at Wauwatosa, Wise. 



