48 PROF. E. TT. CLATPOLE OX PTEEASPIDIAIS- EISH EN" 



8. On the recent DiscoyePvT of Pteeaspidian- Eish in the Uppee 



SlLIJEIAI?- EOCES of I^ORTH A^IEEICA. Bj Piof. E. W. ClATPOLE, 



B.A., B.Sc. (Lond.), E.O.S., Buchtel College, Akron, Ohio. (Eead 

 December 17, 1884.) 



The fossils wHch form the subject of this paper possess consider- 

 able interest to the palaeontologist for three reasons : — 



1. They are the only forms of the Unci yet announced from the 

 Western Continent. 



2. They are the first authentic fish-fossils yet found in the 

 Silurian rocks of America, all previously-reported discoveries of a 

 similar nature having proved erroneous in consequence of zoological 

 or stratigraphical errors. 



3. Some of them are the oldest fish and, consequently, the oldest 

 vertebrates yet discovered in any part of the world, with the possible 

 exce]3tion of Pander's " Conodonts," which are, however, not yet 

 generally received into the class of Fishes. 



The oldest fish-remains already known from this continent are 

 those of the Corniferous Limestone of Ohio and of the Lower 

 Devonian, near the mouth of the Gulf of St. Lawrence, in Canada. 

 Palseontologically, the latter of these appears to be the earlier. The 

 Corniferous Limestone of Ohio yields Macroi^etalichthys, Dinichthys. 

 Onychodus, and allied forms, with a single specimen attributed to 

 Coccosteus ; but the Canadian beds contain Coccosteus, Cephalaspis, 

 and Ctenacanihus, or a form assigned to that genus. 



These, however, are all Devonian fossils, and need not detain us 

 longer. iN'o Silurian fish have yet been obtained in America. 



Galicia has yielded at least one species from rocks considered to 

 be Upper Silurian, the nature of which justifies the age assigned to 

 it. This was the specimen upon which Dr. EJner, in 1847, based 

 his memoir establishing the genus Pterasjns. He considered it the 

 internal bone of a Cephalopod ; but later writers have controverted 

 his opinion, and consider the fossil a genuine fish. Prof. Lankester 

 has named it Scajphaspis Kneri. 



But the fish-fauna which for extent and antiquity claims the 

 first place is that of the English Ludlow rocks. The " Bone-bed '" 

 of the Upper Ludlow has yielded two distinct forms besides frag- 

 ments indicating others, and of one of these forms a single specimen 

 has been obtained from the Lower Ludlow, a fact which, as Prof. 

 Lankester remarks, enormously increases its age. 



Of these Ludlow fossils, one kind consists of small spines with 

 fiuted surfaces, resembling those borne by Selachian or Siluroid 

 fish. To one of these classes they were accordingly attributed by 

 Agassiz, under the names of OncJius Murchisoni and 0. tenvAstriatus. 

 Similar forms occur in Pennsylvania ; these I propose to call Onchiis 

 jpennsylvanims (see fig. 5, p. 61). 



