64 



is the locality from which it is said to have been de- 

 rived. * 



As we have not been able to find any detailed ac- 

 count of this species, we have admitted both it and 

 the genus to which it is said to belong into our Mo- 

 nograph exclusively on the high authority of Profes- 

 sor Brongniart, as quoted in the Manual of Geology. 

 We are not ignorant of the species of Trilobites found 

 near Schenectady, and if permitted to offer a sugges- 

 tion on this subject, it would be, that the description 

 of the American ogygia, was made out by its distin- 

 guished author from the fragment of an Isotelus. 

 The Isotelus is not uncommon in that vicinity, and 

 one of its extremities might, even by a very close 

 observer, be mistaken for that of an Ogygia espe- 

 cially by those who are not perfectly familiar with 

 the Isotelus. 



GENUS ISOTELUS. Dekay. 



This fine genus of trilobites was established No- 

 vember, 1824, by my friend James E. Dekay, M. D. 

 It embraces a considerable number of species so 

 analogous to each other, that except in a very few 

 cases, it is exceedingly difficult to point out their dis- 

 tinctive characters. Some of the species of Isotelus, 

 appear to have reached a greater size than any other 

 trilobite. In the cabinet of P. A. Browne, Esq., there 

 is the fragment of one, which must have been four- 

 teen or fifteen inches long. 



The Isotelus is found in several parts of North 



