272 THE CHICAGO ACADEMY OF SCIENCES. 



Pygidium sub-semicircular, twice as wide as long; the axis 

 sharply defined, occupying one-third the width of the pygidium 

 at its anterior extremity, tapering posteriorly to the narrowly 

 rounded extremity which does not reach the posterior margin, 

 marked anteriorly by two faint annulations; the pleura slightly 

 flattened adjacent to the axis, sloping laterally with a gently 

 convex curve to the margins, anteriorly they bear two faint 

 annulations, but posteriorly they are smooth. 



Remarks. The genus Phacops is not a common member of 

 the Silurian faunas of America, Hall's P. trisulcatus from the 

 Clinton beds of New York .and Fcerste's P. pidchellus from the 

 Clinton of Ohio and Tennessee being the only species which 

 have previously been described. Kindle* has illustrated several 

 specimens of heads from the Niagaran limestone of northern 

 Indiana which he compares with P. pulchellus, but they much 

 more closely resemble the species here described as P. handwerki, 

 though two of his figures show the genal angles to be sharper 

 than in the Chicago specimens; the pygidium illustrated by the 

 same author is much more strongly segmented than P. hand- 

 werki. Fcerste's original illustrations of P. pulchellus show a 

 form with the base of the glabella much more contracted than 

 the Chicago species, and with the pygidium much more strongly 

 segmented on both axis and pleura. 



The nearly perfect specimen illustrated on plate xxiv was 

 collected by Mr. J. H. Handwerk of Joliet, after v whom the 

 species is named. 



Locality. Chicago Drainage Canal, near Lemont. 



Genus 21. DALMANITES Emmrich, 1845. 



Entire body sub-oval in outline, generally angular poster- 

 iorly. Cephalon sub-crescentiform, the genal angles usually 

 produced into spines; glabella prominent, broadest in front, 

 with three pairs of well-marked lateral furrows; cheeks large 

 with clearly defined facial sutures; eyes large and prominent, 

 coarsely faceted. Thorax with eleven segments, axial furrows 

 well-defined, axis strongly convex and narrower than the pleural 

 lobes. Pygidium large, usually sub-triangular, the posterior 

 extremity frequently pointed or mucronate ; axis prominent 

 with numerous segments. 

 Dalmanites plat \caudatus, n. sp., pi. xxv, figs. 35. 



Description. Entire body sub-ovate in outline, with a long 

 caudal spine. Cephalon depressed-convex, semi-elliptical in 



*28th Ann. Rep. Dep. Geol. and Nat. Res., Indiana, p. 484, pi. 24, figs. 9-12. 



