Monograph of the Crustacea of the Cincinnati Group. 129 



furrow parallel with the margin, the upper portion thickest, prolonged 

 beyond the posterior, and terminating in a long spine, deflected at a 

 considerable angle backward ; pygidiiim small, semi-circular, axis very 

 short, of two joints, sides flat, with but one segmental furrow, ending 

 in a long spine at the margin of each side, the rest of the margin with 

 many smaller spines." 



Acidaspis crosotus. — (Locke, 1842,) as defined by Meek. 



Body small, with a general subovate or sub-elliptic outline, rather 

 distinctly convex ; cephalic shield sub-semi-circular, and rather moi-e 

 convex than the body, apparently rounded in front, with the lateral 

 angles produced into slender, mucronate, somewhat curved spines, 

 that extend obliquely outward and backward to points opposite the 

 fifth or sixth thoracic segment ; glabella, including the neck segment, 

 one third longer than wide, with an oblong sub-elliptic outline, the 

 widest part being slightly behind the middle and between the eyes ; 

 lateral lobes, two on each side, of slightly oval outlines, with their 

 longer diameters directed a little obliquely outward and forward, the 

 posterior one being slightly larger than the anterior, while both are 

 separated by as well defined furrows from the central, rather narrow 

 part of the glabella, as they are separated from each other, or from 

 the cheeks on each side ; anterior lobe about as large as all four of 

 the lateral lobes, twice as wide as the narrowed central part of the 

 glabella behind it, and apparently rounded in front ; between the 

 lateral lobes and each eye a kind of outer or supplementary lobe, or 

 protuberance, as large as each two of the lateral lobes, occurs ; while 

 from the outer side of each of these protrudes the small prominent 

 palpebral lobe, which arrangement places the small eyes quite remote 

 from each other ; eyes unknown, but apparently small, prominent 

 and directed laterally; movable cheeks not well preserved in the 

 specimen studied, but apparently narrow, and sloping abruptly froin 

 the eyes laterally; neck segment comparatively large, prominent, 

 with a central tubercle, and well defined by the neck furrow, which 

 arches forward in the middle. 



Thorax nearly twice as long as the cephalic shield, and about one 

 fourth wider than long, exclusive of the produced extremities of the 

 pleurae, with its segments strongly arched upward, but not forward. 

 Lateral lobes, comparatively, rather depressed, and rounding oflf grad- 

 ually toward the lateral margins ; pleurse terminating in mucronate 

 spines, directed outward and more or less backward, the posterior ones 

 being longer, and directed more nearly backward. 



