Mono(jraph of the Crustacea of the Cincinnati Group. 131 



shell or exterior covering, but it is a good representation of the cast of 

 almost every part of the bocl\', and, from its appearance, there can he 

 but little, if any, doubt that figures 3, 4, 6, and 7, on plate 14, of the 

 Ohio Paleontology, belong to the same species. 



The body is sub-circular in outline, granulous, and surrounded with 

 spines ; length, one and oue tenth inches; width, nine tenths inch. 



Cephalic shield more than twice as wide as long, margin thickened 

 and spinous lateral angles, produced into long, slender spines. Length 

 of cephalic shield, four tenths inch ; width, nuie tenths inch, and lengtli 

 of spines surrounding margin, one tenth inch. Glabella, with two lateral 

 lobes on each side, and i)rojecting poiteriorly, showing where the spine 

 attached, which projected back over the middle lobe of the trilobite. 



The glabella, with this projecting spine, is the part of this trilobite 

 most frequently found, and was known here by the name of Acidaspis 

 crosotm (Locke) previous to the application of that name by Prof. 

 Meek to another species. It is most likely that Prof. Locke described his 

 species from fragments of this species, though he may also have had 

 before him fragments of the form to which his name has been confined 

 by Prof. Meek. It is better now to retain the names as suggested by 

 Prof. Meek than to change them, because there is nothing lost by so 

 doing. Prof. Meek suggested that if this spinous glabella should be 

 found to belong to a species distinct from the Acidaspis Cincinriatiensis, 

 it might be called the Acidaspis Bhyncocephalus, but,' as it is now evi- 

 dent that it belongs to this species, the proposed name Acidasjiis 

 JRhyncocephalus may be striken from the list of names. 



The thorax consists of nine segments, without the neck segment, 

 each of which has a depression on the anterior margin, giving a double 

 appearance ; this forms an exception to all other species in this genus, 

 which have only eight segments. The middle lobe is strongly convex, 

 and ^^oth inch in width. The lateral lobes are flat and the pleurte ter- 

 minate in spines about jotli of an inch in length, ^yllich curve outward 

 and backward. The anterior margin of the pleurte terminate in a short 

 spine. The length of the thorax is A inch. The following is the de- 

 scription of the pygidium and part of the thorax, by Prof. Meek : 



Pygidium, exclusive of its spines, about three times as wide as long, 

 and approaching a sub-semi-circular outline ; its anterior margin being 

 straight all the way across, and about one third of its posterior margin 

 in the middle transversely truncated, while on each side of this the pos- 

 terior lateral margins are straight to the anterior lateral angles ; mesial 

 lobe prominent at the anterior end, where it is about as wide as each 

 lateral lobe, but, becoming rapidly depressed and narrowed posteriorly, 

 composed of only two well defined segments ; lateral lobes flat, except- 



