Monograph of the Crustacea cf the Cincinnati Group. loo 



backward, to their falcate extremities, whicli lap upon each other in 

 rolled up specimens, about half their breadth, each a little thickened 

 and divided at its inner end, by a short oblique furrow, into two little 

 subnodose prominences. 



Pygidium small, transversely sub-elliptic, being twice as wide as 

 long, and broadly rounded in outline behind ; axial lobe small, and 

 composed of three obscurely defined segments ; lateral lobes large, and 

 composed each of three segments, which terminate at the margin in 

 moderately prominent, somewhat thickened digitatious, the anterior of 

 which are largest, somewhat carinate on top, and strongly curved 

 backward, wdiile the others decrease in size inward to the central two, 

 which are smallest. 



Surface finely and obscurely granulated, excepting that of the cheeks, 

 which is sometimes marked with very small pits. 



Length of the largest known specimen, 2.15 inches; length of head, 

 0.62 inch; breadth of head, 1.22 inches; length of thorax, 1.1-') 

 inches; breadth of thorax, 0.60 inch ; length of pygidium, 0.37 inch ; 

 breadth of pygidium, 0.65 inch. 



One or two good specimens have been found at Richmond, Indiana, 

 and one or two other specimens in the upper part of the Cincinnati 

 Group elsewhere, but it is so extremely rare that it will never orna- 

 ment many cabinets. 



Fifth subfamily Asaphime — (McCoy). 



PleurjB bent down at the end, and having distinct trigonal facets; 

 thoracic segments eight to thirteen. 



This subfamily may be looked upon as the type of the entire grouj), 

 and contains the most perfectly organized trilobites. They all have 

 the power of rolling themselves into a ball, and they are the only trilo- 

 bites having the triangular facets at the anterior part of the extremi- 

 ties of the pleurae. They have a compact, ovate forni, and from the 

 deflection of the margin all are of considerable depth. 



This subfamily includes the genera Asaphus, subgenus Isotelus, Caly- 

 mene, Dalmanites, Triaiihrus, etc. • 



Genus Asaphtis. (in a wider sense than BRO>fG, by McCoy). 



Head and tail nearly equal; eye's w-ith a firmly fixed, thick cornea, 

 wnth a smooth external surface ; ficial suture cutting the posterior mar- 

 gin of the cephalic shiejd within the lateral angles ; thorax with eight 



