230 CRUSTACEANS. 



Acidaspis halli Shuxmaed. 



Plate xxxii, fig. 4. 



Acidaspis halli Shumard, 1855: Geol. Sar. Missouri, A.nn. Rep., p. 200, 

 pi. B, figs. 7a, b, c. 



Small ; glabella moderately convex, somewhat wider than 

 long ; frontal border somewhat elevated, with the posterior 

 limiting furrow rather deep, and ornamented by a row of large 

 granules ; dorsal sinuses deep ; median portion raised somewhat 

 above the lateral lobes, with a broad frontal lobe which occu- 

 pies about one-fourth the entire length ; occipital sinus well 

 defined, though rather shallow. Fixed cheeks narrow. Mov- 

 able cheeks of medium size, with well-marked border, pro- 

 duced behind into a rather long, somewhat curved spine ; margin 

 with about 14 short, spinous processes, those in front quite 

 short, those behind five or six times as long as the anterior 

 ones. Thoracic segments with the axial portion considerably 

 narrower than the lateral lobes, which are produced into long 

 stout spines. Pygidium small, with the median portion made 

 up of two annulations ; lateral lobes rather flattened, with a 

 single distinct ridge, which broadens toward the margin of the 

 last piece and extends into a long curved spine on each side. 



Horizon and localities. — Lower Silurian, Cape Girardeau 

 limestone: Cape Girardeau. 



Calymene senaria Conrad. 



Calymene senaria Conrad, 1841 : Ann. Rept. Greol. New York, p. 44. 

 Calymene senaria Hall, 1847: Palae. New York, vol. I, p. 23S, pi. Ixiv, 



figs. 2a-n. 

 Calymene senaria Meek, 1875: Geo!. Sur. Ohio, False, vol. I, p. 173, pi. xiv, 



figs. 14a-f. 



Subovate, length about one and one-half times the breadth, 

 height rather more than one-third the breadth. 



Cephalic shield as seen in a direct view from above sub- 

 semi-circular, approaching sublunate, the anterior outline being 

 more or less nearly regularly rounded, and the posterior broadly 

 sinuous, with the posterior lateral extremities bluntly sub-an- 

 gular, or abruptly rounded. Glabella more prominent than the 

 cheeks or eyes, about as wide behind as its length, including 



