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THE AMERICAN NA TURALIST. [Vol.. XXXVII. 



in situ ? Or lias he found detached appendages positively deter- 

 minable as belonging to Tremataspis, to the exclusion of all 

 other accompanying fossil remains? Professor Patten answers 

 the first of these interrogatories in the negative, the second 

 affirmatively. He has obtained in all four detached plates of 

 small size and mediocre preservation, which he regards as 

 portions of as many "paired cephalic appendages" ; these he 

 figures of ten times the natural size and describes in praiseworthy 

 detail. But by what process of reasoning he is able to identify 

 them as belonging indubitably to the genus Tremataspis he does 

 not take the trouble to state, leaving the reader to take it for 

 granted that his determination is correct. 



Not all readers, however, will be prepared to accept a deter- 

 mination so utterly at variance with analogy. On the contrary, 

 rational students will maintain that inasmuch as certain fish 

 fragments are identifiable as parts of jointed oarlike appendages, 

 that fact is prima facie evidence of their pertaining not to Trem- 

 ataspis, but to an entirely different order of Ostracophores — 

 the same to which Pterichthys, Bothriolepis and Asterolepis 

 belong. This indeed was the view taken by Pander as early as 

 1856, who, so far from associating certain fragmentary append 

 ages from the Baltic Silurian with Tremataspis, referred them to 

 the Pterichthyid order, whose presence in those beds is not 

 otherwise indicated. This procedure is entirely justified by the 

 tact that structures of this nature are known to' be present in the 

 group typified by Pterichthys, but not in that to which Trema- 

 taspis and Cephalaspis belong. The danger of a reliance on 



association of detached fragments is well illustrated by Cope's 

 confusion of an appendage of Bothriolepis with Holonema 

 remains,' certainly no trifling error, and other instances are but 



