24 PALEONTOLOGY. 



abruptly contracted (almost entirely on the posterior side) into slender, 

 rounded, very sharp spines, which curve backward and outward. Each of 

 the pleurae is also provided with a broad, rather deep, flattened furrow, 

 which commences near the inner end, and extends straight outward for 

 some distance, with parallel sides, but gradually tapers, mainly on the ante- 

 rior side, to a lanceolate point, before reaching the free extremities. These 

 furrows have not the obliquity usually seen in those of Paradoxides, but run 

 parallel to the direction of the pleurse, so as to leave a slender straight ridge 

 of equal size along the anterior and posterior margin of each rib. 



The pygidium, exclusive of the portions of the free border broken away, 

 has a nearly semicircular outline, being about twice as wide as long, while 

 it is as much flattened as the thorax. The part remaining equals in length 

 the five thoracic segments next in advance of it. Its mesial lobe is much 

 depressed, and about three-fourths as wide anteriorly as the breadth of 

 that of the thorax at its widest part seen. Posteriorly it tapers moderately, 

 and extends nearly the entire length of the pygidium, as seen with the free 

 border broken away. It is evident, however, that the flattened border pro- 

 jected more or less behind its termination. It shows distinctly five seg- 

 ments, Avith indications of about two others at the posterior end. The 

 lateral lobes have each three segments, the anterior one being extended out 

 nearly parallel to those of the thorax, Avliile the others are directed more 

 obliquely backward, and rapidl}^ widen outward. Like the pleurse, they 

 have each a broad, flattened furrow; that of the anterior one being nearly 

 parallel to those of the pleurse, while those of the other two are directed 

 more obliquely backward, particularly the posterior one, which is almost 

 parallel to the longitudinal axis of the body. These furrows are so deep 

 and broad as to give the three segments of each lateral lobe the appearance 

 of six irregular ridges; the irregularity being produced by the posterior two 

 furrows, instead of passing along the middle of each segment, being curved 

 backward so as to divide it very unequally, leaving the anterior part much 

 the broader. No fine surface-markings are preserved on the specimen. 



Entire length of the imperfect specimen, nearly 3 inches, of which the 

 remaining 8 thoracic segments form 1.70 inches; breadth of the thorax, exclu- 

 sive of the free spiniferous ends of the pleurse, 2.05 inches, and, including 



