tRENtON LIMESTONE. 233 



horns or processes of this organ are flat on the outside, and angular on the inner side. The 

 crust of the lower side of the head, as above, shows a longitudinal suture extending down 

 the middle to the point of junction at the epistoma, but it does not continue into this organ. 



Fig. 7 A. The central lobe of the cephalic shield. 



Fig. 7 t. The same part of a larger individual. Specimens of this kind are very frequently found, and 

 are sometimes mistaken for parts of other trilobites. The lateral or maxillary lobes of the 

 buckler often remain connected, while the central portion is separated at the suture. 



Plate LXL 



Fig. 3 a. The buckler of an individual of medium size. This is more extended in front, and the eyes 

 are more prominent than usual. 



Fig. 3 b. Tho caudal shield, corresponding in size to the buckler. The crust is removed, showing the 

 lines of the articulations. 



Fig. 3 e. A portion of the surface of the buckler enlarged, showing a peculiar punctate structure which 

 is scarcely visible to the naked eye. 



Fig. 3 d, e. Lateral and dorsal view of a small perfect specimen. The figure preserves all the important 

 marks of the species. The buckler is somewhat compressed or bent in front, so that the facial 

 suture is not shown to its full extent This specimen is from Kentucky. 



{Cabinet of W. H. Pease.) 



Fig. 3 / Buckler of an individual of ordinary size. The eyes are prominent, but less proportionally 

 elevated, and the whole less convex than the specimen 3 a. The course of the facial suture 

 is distinctly vi.iible. 



Fig. 3 g. Caudal shield corresponding in size to the buckler 3 / The marks of the transverse segments 

 scarcely visible. 



Fig. 3 A. View of the eye of 3 / natural size, as seen looking forwards and outwards. 



Fig. 3 t. Oblique front view of the eye, which, under ordinary magnifying glasses, presents no granula- 

 tions. 



Fig. 3 k. The labrum or epistoma, showing the inner or upper side. 



Fig. 3 m. A portion of the same enlarged, showing the striae upon the surface^ 



Fig. 4 a, b, c. Front, lateral, and dorsal views of the original specimen, to which Green applies the 

 name of /. cydops. Its proportions vary in no essential manner from other individuals of 

 /. gigas. It is abruptly bent downward before, and the sides of the buckler are worn ofT, 

 giving it the appearance of being narrower than usual. The whole specimen is much worn, 

 and the crust almost entirely removed. The bases, only, of the eyes remain, which are round; 

 but this is true of all the others, when worn off in the same manner. 



Plate LXII. > 



Fig. 1 a. A specimen folded so that the two extremities meet. The fossil is rarely found in this condition ; 

 and in many instances where it has originally assumed this form, it has been subsequently 

 crushed. 



Fig. 1 b. The caudal shield of a young individual, showing the marks of the articulations, and pre- 

 serving the trilobate form more perfectly than older specimens. 



Fig. 1 e. A magnified portion of the surface of one of the articulations of a large individual, showing, 

 in addition to the punctures upon the surface, a series of curving impressed lines. The latter 

 [ Palaeontology.] 30 



