FOSSILS OF THE KEOKI'K GROUP. 527 



about midway between the lateral angles and the neck seg- 

 ment, but nearer the latter. Thorax nearly as long as the 

 glabella, exclusive of the neck segment, distinctly tribolate ; 

 axil lobe slightly wider than the lateral lobes, rounded and 

 rather prominent; its segments narrow and straight, or not 

 arched forward. Lateral lobes more depressed, somewhat 

 flattened on the inner side, rounding down to the lateral 

 margins; segments duplicated by a nearly mesial furrow 

 extending from their inner ends out to or a little beyond 

 the undefined knee, beyond which they are obliquely flat- 

 tened for folding together, and rounded at their extremities. 

 Pygidium a little more than one-fourth wider than long, 

 rather distinctly convex, rounded behind, and more or less 

 straight in front, with anterior lateral angles obliquely 

 truncated and a little rounded. Mesial lobe very promin- 

 ent and well defined, rounded above, and a little flattened 

 or furrowed on the sides ; as wide anteriorly as the lateral 

 lobes, tapering and declining somewhat posteriori}- to an 

 abrupt, obtuse, prominent termination; about half its own 

 greatest anterior breadth within the flattened margin ; seg- 

 ments fourteen or fifteen, distinctly defined, smaller than 

 those of the thorax. Lateral lobes depressed below the 

 mesial lobe, somewhat flattened on the inner side, and slop- 

 ing to the rather narrow and more flattened border ; seg- 

 ments ten. some what oblique, well defined for three-fourths 

 of the distance out. and thence less distinctly so, to within 

 a short distance of the margin ; a few of the anterior ones 

 with an obscure longitudinal furrow. Surface granular, 

 the granules being largest on the posterior portions of the 

 glabella, palpebral lobes and neck segment. On the seg- 

 ments of the axial lobe, both of the thorax and pygidium, 

 a^ well as on those of the lateral lobes, they are very small, 

 and regularly disposed, so as to form a single row on each 

 segment. 



Entire length, 1.19 inches; breadth of head, about 0.80 

 inch; length of pyiddiuni, O.H inch; breadth of do., 0.56 



