144 .Monograph of the Crudacea of the Cincinnati Group. 



Thorax with the axial lobe highly convex, and the lateral lobes 

 strongly geniculate, subequal in width, rapidly tapering posteriorly 

 from the fourth or fifth segments. Segmentg curved forward on the 

 top of the axial lobe, and the furrows on the pleura strongly marked. 



Pygidium obtusely pointed behind, the lateral borders inclosing an 

 an angle of about 120°, the anterior border rounded; the number of 

 articulations not clearly defined, but apparently numbering about ten 

 or twelve, besides the terminal one ; those of the lateral lobes have been 

 more numerous. The entire surface finely pustolose. 



Not found at Cincinnati, but found in Warren county, in the upper 

 part of the Cincinnati Group. Sometimes found rolled up and some- 

 times extended. Extremely rare. 



Genus Prcetus — (Steininger, 1831). 



Cephalic shield semi-circular, surrounded by a thickened margin ; the 

 jiosterior angles do not project perceptibly ; the glabella is very con- 

 vex, parabolic, rounded at the anterior part, undivided, without any 

 lateral lobes ; at the posterior part it is- as broad as the margin, to 

 which it is immediately joined. The facial suture projects over the 

 anterior cephalic margin on a line with tlie eyes, is thence directed 

 toward the eye, forms the covering plate, and runs at first straight, 

 afterward in an S-shaped curve, to the posterior margin, which it 

 penetrates beyond the center, in an .oblique direction toward the ex- 

 ternal part. Eyes of moderate size, very prominent, smooth, joined 

 rather closely to the glabella. Body axis ten-jointed, the joints grad- 

 ually more narrow toward the posterior part, strongly arched, abruptly 

 separated from the lateral lobes by a peculiar furrow, these lobes having 

 an oblique indentation. 



" Caudal shield corresponding with the cephalic, but smaller, the 

 axis highly arched, short, distinctly articulated, the sides furnialied with 

 slight furrows or obsolete ribs, the margin even, but having a very 

 acute angle. The surface of the shell almost smooth, but with distinct 

 traces of granulation on the glabella, and on the cheeks beneath the 

 eye." 



Prcetus parviusculus — (Hall, 1866). 



Body, in. general form, broadly ovate, widest across the base of the 

 cephalic shield. Head sublunate, produced into long, sharp spines at 

 the posterior angles of the cheeks. Glabella elevated, broadly sub- 

 comical, rounded in front, concave behind ; furrows not visible. 



