Monograph of the Crustacea of the Cincinnati Group. 141 



men of this species. I come to this conclusion from the description, 

 the place where found being the Cincinnati Group, and from the en- 

 graving in Burmeister's INIonograph of trilobites ; indeed, I do not 

 believe there is any doubt about it. I know no reason why the 

 fossil should not retain the name callicephala (beautiful head), instead 

 of the name senaria, nine years later, and much less expressive. 

 But the paleontologists of the whole country seem to have adopted the 

 name senaria, and as there may be some reason for it that I do not un- 

 derstand, I have retained that specific name instead of callicephala 

 (Green), in deference to their action or judgment, as the case may be, 

 and against my own opinion ot what ought to be the rule of action. 



Cahjmene Christyi — (Hall). 



General form elongate ovate, symmetrical ; body gibbous, the 

 pygidium equaling the length of the head. Head semi-circular, the 

 frontal border expanded, and gradually narrowing on the sides ; the 

 posterior angles terminating in a short, sharp spine. Glabella wide, 

 slightly narrowing toward the front, regularly convex, strongly defined 

 by the dorsal furroAvs, a little concave in the middle of the base ; 

 occipital furrow well defined, nearly straight, and in right line with 

 the cheek furroAvs ; posterior furrow oblique, defined, but not deep ; 

 the middle one nearly rectangular to the axis, while the anterior one 

 is but slightly indented. The posterior lobe is much wider than the 

 middle one, and about the same width as the anterior one. Cheeks 

 small. Eyes very prominent. 



Thorax with thirteen segments ; the axis salient, and a little wider 

 in the middle than the lateral lobes ; the articulations of the latter 

 flat, or slightly curving, for a little more than one third their length, 

 when they are suddenly bent downward. 



The pygidium is gibbous, semi-elliptical, with the axis very prom- 

 inent, and marked by seven or eight rings, the last one being longer 

 and more prominent, with a minute, scarcely defined node at the 

 extremity ; lateral lobes marked by six flattened ribs, the last one of 

 which is minute, the expansion being continued in a narrow, flattened 

 border around the posterior extremity. 



It is distinguished by the form of the glabella and the shallow fur- 

 rows Avhich leave the lobes flattened, and not convex and rounded, and 

 and by the minute spine at the posterior angle of the head shield. 



Found near Oxford, in the upper part of the Cmcinnati Group, and 

 named in honor of Prof. Christy. 



