30 NEW YORK STATE MUSEUM 



Neither in this species nor in Cyathaspis has the presence of paired 

 appendages been definitely determined, notwithstanding that claims have 

 occasionally been made as to their occurrence. According to Dr Bashford 

 Dean, who examined Professor Claypole's type material, the specimens 

 which were regarded by their original describer as fins are probably crushed 

 Elasmobranch spines which have become accidentally associated with the 

 thoracic region of the shield. Hence, the published figure of Claypole's 

 restoration, which reappears from time to time in geological textbooks, is 

 obviously misleading. The supposition that one or more pairs of append- 

 ages were present in Tremataspis, advocated in several of Professor Patten's 

 papers,' is purely gratuitous, and contrary to probability. The perforations 

 in the shield which this author thinks may have served for the attachment 

 of swimming organs are interpreted as branchial orifices by the majority of 

 writers. 



Occasionally one meets with the statement, as for instance, in Dr O. P. 

 Hay's valuable Catalogue of Fossil Vertebrata from North America, that the 

 species under discussion occurs in the Devonic of Pennsylvania, an error 

 which is perhaps attributable to confusion of formation names. The term 

 " Onondaga group," as used by Claypole, was not intended to apply to the 

 Mesodevonic Onondaga limestone, but to the beds formerly known as the 

 "Onondaga salt group," now more generally termed the Salina. The 

 horizon of these beds corresponds with that of the English Ludlow, or with 

 the interval between that and the Wenlock. According to the Pennsyl- 

 vania reports, the whole mass of the Salina shale in Perry county is about 

 1500 feet in thickness, and for the most part, with the exception of these 

 fragments of Palaeaspis and the spines of Onchus, entirely unfossiliferous. 



' On the Structure and Classification of tlie Tremataspidae. Am. Nat. 1902. Tfi: 379- 

 93, and Imp. Acad. Sci. St Petersburg Mem. 5. Ser. 8, v. 13, 1903; On the Origin of Ver- 

 tebrates, with Special Reference to the Structure of Ostracoderms. Verhandl. V. Internal. 

 Zoologen-Congresses zu Berlin, 1902 ; On the Appendages of Tremataspis. Am. Nat. 

 1903. 37:223-42. 



