228 CRUSTACEANS. 



Cyphaspis glrardeauensis Shumard. 



Plate xxiv, fig. 2. 



Cyphaspis glrardeauensis Shumard, 1855 : Geol. Sur. Missouri, Ann. Rep. 

 p. 197, pi. B, figs, lla-b. 



Ovate, depressed. Cephalic shield semicircular, forming- 

 more than one-third the length of the body, very moderately 

 convex ; exterior border raised, narrow, prolonged posteriorly 

 into slender curved spines, which extend back to the seventh 

 thoracic segment ; within the border is a narrow well-defined 

 groove, and between this and the furrow which passes round 

 in front of the glabella is a slightly raised surface. Glabella 

 subovate, rounded in front, truncated behind, and occupying 

 rather more than two-thirds the length of the head ; greatest 

 width a little in advance of the middle ; surface moderately 

 convex and but little elevated above the cheeks ; at the base 

 on either side is a small ovate tube, about half the length of 

 the glabella, and entirely separated from it by a narrow, deeply 

 impressed groove ; longitudinal furrows narrow, profound^ 

 uniting in front of the glabella ; occipital furrow straight, nar- 

 row, deep ; occipital annulation about as high as the glabella, 

 wide in the middle, narrowing toward the extremities, with a 

 small central tubercle. Cheeks depressed, convex ; eyes small,^ 

 nearly circular, situated close to the glabella and opposite to 

 the anterior half of its lateral lobes. Thorax with ten seg- 

 ments, with strongly marked longitudinal furrows ; median 

 lobes wider than the lateral lobes, slightly flattened in the mid- 

 dle, rings slightly arched toward the front, separated by strong 

 furrows ; seventh segment provided with a long slender spine 

 extending backward beyond the posterior margin of the pygi- 

 dinm. • Tail piece semicircular, twice as wide as long ; border 

 narrow; axial lobe with about seven segments. Surface glab- 

 rate. 



Horizon and localities — Upper Silurian, Girardeau lime- 

 stone : Cape Girardeau. 



