DESCRIPTION. 



The following described fossils have been obtained from the Trenton 

 limestone since the publication of the first volume on the Palaeontology 

 of New- York. Several of these are entirely new, and interesting, as 

 adding to our knowledge of several genera, of which few species have 

 yet been described. These fossils were collected during a short excur- 

 sion in a few localities not thoroughly examined, and from these we 

 may infer that a large number yet remain undescribed in the lower Silu- 

 rian rocks. In these descriptions I have not included several, the char- 

 acters of which are somewhat equivocal, or of which we may expect to 

 procure more perfect specimens. Several specimens, illustrating in a 

 more perfect and satisfactory manner species already described in the 

 volume referred to, have been added to this list, in order to give those 

 pursuing the study of this subject the best information we possess up to 

 this time. 



In commencing a work like the Palaeontology of New-York, in a 

 country where comparatively so little had been done in collecting or in- 

 vestigating fossils of the older rocks, it was impossible in all cases to 

 procure perfect specimens of the fossils described. It is expected more- 

 over that the fossils from the older strata are less perfect and more di- 

 lapidated than those of newer formations ; and the solid and sometimes 

 altered condition of the strata often prevents the procuring of perfect 

 specimens, which may readily be done in the more modern formations. 

 It would not be satisfactory to the student, nor even to the cursory ex- 

 aminer, to leave unfigured and undescribed, fragments or imperfect 

 specimens of fossils, since the collection of every one, and particularly 

 of beginners, must necessarily consist in part of such, from the difficulty 

 and time required to obtain perfect ones. It is therefore desirable from 

 time to time to present the additional knowledge acquired by the fortu- 



