120 Monogra'ph of the Crudacea of the Cincinnati Groiip. 



prominent. Surface minutely granulose ; length about 6-100 of an 

 inch, width about 3-100 of an inch. It differs from the B. oculifer in 

 being destitute of the j)romiuent eye tubercle. 



Found at low water-mark, under the bank of the Ohio, at Fulton ; 

 at the excavation for Columbia avenue 160 feet above low water- 

 mark ; on the run back of Plainville, and generally at all exposures be- 

 low 300 feet above low water-mark. It is a common fossil. 



Genus Cythere — (Muller, 1785). 



" Carapace often very convex, especially on the ventral portion ; 

 sometimes smooth and setigerous, generally pitted, and occasionally 

 reticulated ; varying in outline from an acute oval to an irregular ob- 

 long ; in the first case it often resembles a peach-stone in miniature ; 

 in the latter case a central and two posterior tubercles sometimes give a 

 character to the valves ; and in each case the anterior, and sometimes 

 the posterior hinge forms an indistinct angle on the dorsal edge ; the 

 hinge line of each valve occupies about the middle third of the dorsal ■ 

 margin, and presents a ridge or bar and a furrow, the bar on one valve 

 corresponding to the furrow on the other ; the bar is sometimes blended 

 with the edge of the valve, and is occasionally finely crenulated ; it is 

 more or less developed at its extremities into cardinal processes or 

 teeth, which with still stronger, but isolated teeth at the ends of the 

 furrow, on the opposite valve, form the anterior and posterior hinges 

 of the carapace ; the ventral margin of each valve is more or less in- 

 curved near the middle, where its edge is frequently produced (as also 

 occasionally in Cypris) into a thin, projecting, laminae curvilinear plate. 

 The posterior border being always depressed and contracted, and fre- 

 <iuently notched at its dorsal angle, forms a low sub-acute marginal rim 

 or "posterior lobe," of varying breadth." 



CytJiere Cincinnatiensis. — (Meek, 1872.) 



Carapace valves varying from transversely suboval to subcircular ; 

 moderately and rather evenly convex, the greatest convexity being in 

 ike neutral and anterior regions ; without any visible tubercle or nodes ; 

 s'^entral margins rounded or semi-oval, and but slightly unequal or 

 siJiiekened ; anterior and posterior margins more or less rounded, the 

 former being more broadly rounded generally than the latter ; hinge 

 iinargin very short, very slightly sinuous just behind the umbones, and 

 jrojjnding into the posterior margin, so as scarcely to produce any 

 \,yjsible angularity ; umbones, near the anterior, a little tumid, rising 



