t;HAZY LIMESTONE. 25 



This is a very distinctly marked fragment of an undcscribed trilobite ; the distinctness of 

 the false articulations, and deeply trilobate cbarrirter of the caudal extremity, distinguish 

 it from known species of Isotelus, which it resembles in the marginal expansion and general 

 form. 



Position and locality. This fossil is found in tlie crystalline and highly fossiliferous mass 

 of tlie Chazy limestone, below the portion containing Maclurea magna, at Chazy village. 



(Slate Collection.) 



43. 1. ISOTELUS GIGAS1 



Pl. IV. (bis). Fig. IQ. 



Asaphns platycepfiahi.1. Stokes, Trans. Geol. Soc. London, 1S22, Second series, Vol. i. p. 208, pl. 27. 

 Isutelus gigas. Dekay, Annals N. York Lycevim, 1&24. Vol. i. p. 171, plates 12 & 13. 



This fragment approaches so nearly in character to the caudal shields of the young of 

 Isotelus gigas, that I have not thought it worth while to separate it from that species. 



44. 2. ISOTELUS CANALIS. 



Pl. IV. (bis). Figs. 17, IS, 19. 

 Isotelus canalis. Conr.^d in MS. 



Margin of caudal extremity broadly and deeply depressed, forming a channel ; surface 

 ^punctured. Judging from this fragment, the original was at least six inches in length. 



Figs. 18 &. 19. Labrum or epistoma of an Isotelus, perhaps of /. canalis. 



The structure and general aspect of these portions of the trilobite evidently ally it 

 generically with the Isotelus ; and from the discovery of these, I am disposed to admit 

 the species which the fragment before mentioned did not justify. The form of these plates 

 is more elongated, and totally different from the corresponding parts of /. gigas. 



Position and locality. These fragments of a large species of Isotelus occur near the 

 upper part of the mass, a little west of Chazy village. (State Collection.) 



45. 1. CERAURUS? — [ Species undetermined) . 



Pl. IV. (bis). Fig. 20. 



A single fragment, being the posterior prolongation of the buckler of a species of 

 Ceraurus, very analogous to C. pleurexanthemus of the Trenton limestone. 



Position and locality. In the oolitic limestone of Chazy, (State Collection.) 



Remains of other trilobites, too indistinct to be described, have been noticed in this rock ; 

 but the materials are so comminuted, that it is impossible to recognize fossils, of which 

 fragments of many species have been observed. 

 L Paleontology.] 4 



