Vol. 52.] THE BBITI8H SILURIAN SPECIES OP ACIDA8PIS. 235 



II. The British Silurian Species of Acidaspis. By Philip Lake, 



Esq., M.A., E.G.S. (Read December 18th, 1895.) 



[Plates VII. & VIII.] 



Contents. -d 



rage 



I. Introduction 235 



II. Description of Specie9 236 



III. Comparison with the Swedish and Bohemian Faunas 244 



I. Introduction. 



The genus Acidaspis has been a peculiarly unfortunate one in 

 Britain. Several of the specific names which are in common use 

 are manuscript terms, or but little better ; and the species to which 

 they are applied have never been described. It is impossible, there- 

 fore, without access to standard collections, to determine to what 

 forms the names refer. Even the species which have been described 

 have in many cases been imperfectly figured, and the result is 

 endless confusion. The common English trilobite, A. coronata, has 

 received abroad no less than three names, all of them different from 

 ours ; while in England, on the other hand, the foreign name A. 

 crenata is often applied to a species which is quite distinct from 

 the original A. crenata, and which in fact has never yet been found 

 out of Britain. 



The disorder is worst among the Silurian forms, although these 

 are much the most perfect. The Ordovician species are usually 

 fragmentary, but the fragments have been fully described. 



It is the object of the present paper to attempt to reduce the 

 specific terminology to some sort of order, and to rescue the common 

 manuscript names from the obscurity in which such terms tend to 

 become involved after a lapse of time. Only the Silurian forms are 

 here described ; the Ordovician species have been left in the hope 

 that better material may be forthcoming in the future. 



Even the name of the genus itself is matter of controversy. 

 Murchison l employed the term Acidaspis in 1839, and in the same 

 year Emmrich 2 proposed the name OdontopUura. The latter is often 

 used in Germany, but the former is the more widely spread. There 

 is, however, an earlier name still, the use of which has been advocated 

 by Vogdes 3 and J. M. Clarke, 4 though Vogdes, in his bibliography, 3 

 does not adopt his own suggestion. This name is Ceratocephala, 

 and was applied by Warder 6 in 1838 to a species which he called 



1 ' Silurian System,' p. 658. 



2 « De Tril. Diss, inaug.' 1839, Berlin. 



3 Proc. Acad. Nat. Sci. Philadelphia, 1877, p. 138. 



* 44th Ann. Eep. New York State Museum (1891), p. 91. 

 6 Bibl. Pal. Crust. 1893, San Francisco. 



* Amer. Journ. Sci. & Art, vol. xxxiv. no. 2 (1838), p. 377. 



