trenton limestone. 243 



Plate LXV. 



Fig. 1 a. A nearly entire specimen, with the maxillary portions obscure or partially removed. 



This is the orifjinal specimen upon which Prof. Green fonnded the Genus Ceraurbs. 

 The buckler is partially crushed and obscured by soft shaly matter, and the oculiform 

 tubercle very imperfectly preserved. The posterior prolongations of the buckler are distorted 

 and obscure, as are also the spines proceeding from the caudal shield. Although very 

 obscure, a careful examination shows that the structure of the articulations, form and lobes 

 of the glabella, correspond wiiii the better preserved specimens represented in the succeeding 

 figures. 



Fig. 1 J. A specimen of the same partially folded, with the buckler curved forward and the margin 

 broken off The crust is partially exfoliated, so that the surface markings are not well 

 preserved. 



Fig. I c. Front view of the buckler, showing the junction of the epistoma. 



Fig. I d. A large imperfect specimen of the same species, showing more distinctly the peculiar structure 

 of the articulations. The buckler is imperfect, but still partially preserves the posterior spines. 

 The caudal spines are broken off! 



Fig. 1 e. Lower side of the buckler of the last, showing the epistoma joined by a straight suture to the 

 front of the glabella. 



Fig. 1 / A separated labrum, with upper margin broken off, being the form in which they are usually 

 found in the rock. 



Fig. 1 g. A buckler, with the maxillae removed. 



Fig. 1 h, i. The glabellse of two large individuals. Such fragments are very frequently found, while 

 perfect specimens are exceedingly rare. 1 i*. A magnified portion of the surface. 



Fig. 1 /;. A caudal shield, with the spines removed. 



Fig. 1 I. The spines of the caudal extremity, with a single articulation connecting them. View from the 

 lower side. 



Fig. 1 m. The caudal shield, with the spines attached. This specimen preserves the characteristic fea- 

 tures of this part of the fossil in great perfection. The spines are attached to the first segment 

 only, which is enlarged and greatly expanded laterally, and, as it curves downwards, throws 

 out a process above, to which the segments of the thorax are joined. 1 m*. A magnified 

 portion of the surface. 



Fig. 1 n. A transverse section, showing the elevation of a segment, and the lateral extension of the 

 articulations into fin-like processes. 



Plate LXVI. 



The specimens illustrated upon this plate were obtained after the previous plate had 

 been engraved. 

 Fig. 1 a. A fragment of a large individual, preserving the buckler and eight articulations of the thorax. 



The surface is beautifully and evenly granulated or papillose, with larger tubercles upon the 



cephalic shield, and mammillary tubercles upon the articulations. These are enlarged in the 



figures 1 b, c, d. 

 Fig. 1 e. Front view of the specimen 1 a, showing the elevation of the oculiferous tubercles. 

 Fig. 1 / One of these tubercles magnified. When magnified to this degree, they exhibit only rounded 



granulations. 



31* 



