CONTRIBUTIONS TO PALEONTOLOGY. 71 



6. ON THE OCCURRENCE OF CRUSTACEAN REMAINS OF THE 



GENERA CERATIOCARIS AND DITHYROCARIS, 



WITH A NOTICE OF SOME NEW SPECIES FROM THE HAMILTON GROUP AND GENESEE SLATE. 



[With a Plate.] 



The interest attached to the fossil remains of Crustacea other 

 than those of Trilobites, in the palaeozoic rocks, has within a 

 few years been greatly increased by the discoveries in Great 

 Britain and the elucidation given by Messrs. Huxley and Salter, 

 and more recently by the papers of Mr. Salter in the Quarterly 

 Journal of the Geological Society of London. In a late number 

 of this Journal, Vol. xix, Part 1, some species are described from 

 the Coal measures and Devonian rocks of British North America, 

 as well as from the Carboniferous rocks of Great Britain. 



Up to this time, our knowledge of these Crustaceans is chiefly 

 confined to the Genera Eurypterus, Pterygotus and Ceratiocaris, 

 from the Waterlime group ; with a few fragmentary specimens 

 from some rocks below, and others from those directly above that 

 formation. These are all of Silurian age ; and the strata of De- 

 vonian and Carboniferous age, within the United States, have 

 hitherto furnished but meagre and unsatisfactory materials. 



I have for a long time known of the existence of some fragments 

 of DiTHYROCARis from the Hamilton group, and more recently 

 have obtained other fragments which seem referable to the Genus 

 Ceratiocaris. My collections, however, are so imperfect, that I 

 would have deferred any notice of them for the present, but for 

 the hope that publicity might attract the attention of collectors 

 and others to the subject ; by which means we may become better 

 acquainted with the geological and geographical distribution of 

 these crustaceans, and thus obtain materials for their complete 

 illustration in the volume on the Palaeontology of the State. 



The materials before me are chiefly the following : 



1^*. Several fragments from the shales of the Hamilton group, one of 

 which is the tail-joint and appendages : another consists of several joints 

 of the abdomen, with the tail and appendages ; while another preserves the 

 half, or one valve of a strongly marked carapace. 



The two first mentioned specimens are from the same locality, presenting 

 similar characters, and are apparently referable to a single species of Ce- 

 ratiocaris. The carapace presents a different texture and surface-ijiarking, 



