8 HINDE, ANNELID REMAlXS FROM SILURIAN OF GOTLAND. 



toothed plates of difFerent forms and sizes, attached to tlie jaw-sac 

 in close proximity to eacli other. Prof. Ehlebs, in his exhaus- 

 tive monograph ou the »Borstenwlirmer», has divided this 

 family into two principal groups, in one of wliich, tlie Eurn- 

 cea lahidognatlia, the separate plates in tho half of eacli upper 

 jaw are very uneqnally formed, and so placed with regard to 

 eacli other, that in the resting position, the smaller pieces are 

 arranged in a semicircle ronnd the larger; whilst in the other 

 group, the JEmncea prionognatha, the exsertile jaw-plates in 

 the half of each npper jaw are more or less similar and ar- 

 ranged in a row behind each other. To some of the princi- 

 pal jaw plates in existing annelids, distinctive names have 

 been assigned by Ehlers and Clapaeéde, but at present, so far 

 as I am aware, no eqnivalent English terms for these organs 

 have been used, and I propose therefore to employ the follow- 

 ing corresponding terms; (1) Supports = Träyer, Ehlers ; 

 Support, Claparéde. (2) Piucers = Zange Ehlers; Pince, Clap. 

 (3) Large dental plate = Zalinstucke, Ehlers; Piece dentah^e, 

 Clap. (4) Paragnaths == Säge-platten Ehlers: Paragnathes, Clap. 

 The resemblance of many of the fossil specimens to these 

 distinctive jaw plates is so clear, that there is no difhculty 

 in determining their relative positions in the jaw apparatus, 

 bnt at the same time it is quite impracticable to determine, 

 with any reasonable approximation, the particular detached 

 plates which were associated together to complete the jaws of 

 the fossil annelid. This difficulty is at once manifest if an 

 attempt is made for example, to reconstruct from these de- 

 tached fossil jaw plates, the jaw armature of an annelid resem- 

 blinof the existing o-enus Eunice. We find that there are seve- 

 ral of the fossil plates closely resembling the large dental 

 plate and also the paragnaths of the upper jaw, but the halves 

 of the under jaw are wanting, and there are no fossil jaws 

 to correspond closely to the supports and the pincers of the 

 upper jaw, which are present in an existing Eiinice. It is 

 possible that these missing pieces may have been originally 

 present, though they have not yet been discovered, but consid- 

 ering the numbers of the other plates which are present, the 

 absence of these particular portions renders it very imcertain 

 whether the jaw apparatus of these Silurian annelids was com- 

 posed of as many plates as that of the existing genera to 

 which they appear nearest allied. Until some complete forms 



