47 



I am indebted to Professor Eaton, for two speci- 

 mens of this very interesting species. In his Geolo- 

 gical Text Book, he thus describes it: " Tail cres- 

 cent-form, or concavo-convex, with the convex side 

 forward, upon which the post abdomen terminates: 

 abdomen contains about 1 2 articulatious, with an ab- 

 rupt termination equal in breadth to one-fourth of 

 the length of the transverse lunate tail; the articula- 

 tions of the side lobes gradually incline towards the 

 axis of the body, until the last pair terminate at the 

 tail. Found in transition limestone at Glenn's Falls, 

 and Becroft's mountain, near Hudson. I have a spe- 

 cimen from Becroft's mountain, with part of the 

 original covering of the animal remaining." 



When we first noticed the remarkable lunate ap- 

 pearance of the tail of this Asaph, we supposed that 

 it was occasioned by some accident, but there seems 

 no doubt that this conformation is natural. In our 

 specimens of this species, which are not however per- 

 fect, the articulations of the abdomen do not exceed 

 8 in number. The representation of this animal re- 

 main given by Mr. Eaton, plate 1, figure 1, is exceed- 

 ingly inaccurate; it will confuse rather than illustrate 

 the subject. Our cast and the drawing, we believe, 

 are taken from the same specimen, which was kindly 

 loaned by Mr. Eaton for this work. It is but jus- 

 tice to the amiable, industrious, and indefatigable au- 

 thor of the Geological Text Book to remark, that he 

 regrets as much as any one, the insufficiency of his 

 figures of the trilobites, to give any correct idea of 

 the fossils they are intended to represent. 



