LUDLOW FORMATIONS OF THE WEST OF EXGLAXD. 369 



suffered more injury than iu the deposits of finer material. There 

 are in these same Upper Ludlow strata the shelly tubes of Serpu- 

 imlites longissimus, Murchison, and the transversely striated 

 riband-like markings of Trachyderma coriaceum, Phillips, both of 

 which forms have been referred to Annelids ; but I have not met 

 with any of the jaws in such juxtaposition with either of these 

 fossils as to give ground for the supposition that they may have 

 belonged to the same animals. 



In respect to the condition in which these jaws occur, there is a 

 close correspondence with the American forms. They are composed 

 of the same brittle chitinous material, and when unweathered they 

 have the same glossy black lustre. Unfortunately, also, they have 

 been similarly detached from their natural positions and indivi- 

 dually scattered in the muddy sediments, so that there is the same 

 difficulty about their satisfactory classification. In addition to the 

 minute bodies which can be definitely determined to be portions of 

 the mouth-apparatus of Annelids, there are on some of the rock- 

 surfaces numerous minute, dark, chitinous fragments, of no definite 

 shape, which are not improbably portions of the skin of the same 

 animals. Similar fragments are also present in some of tho Ame- 

 rican rocks ; and if they are rightly referred to the horny integument 

 of these Worms, these animals must have possessed a greater amount 

 of chitin in their skins than their modern congeners, whose body- 

 covering is of such a delicate character as to render it very unlikely 

 to leave any traces in the fossil state. Judging from the quantity 

 of these fragments, and the number of the jaws, the Errant Annelids 

 must have been very abundant, at least locally, in the Silurian 

 period. 



Whilst there is a similarly great variety of fhnn in the English 

 fossil jaws, there is no striking diff'erence from those already described 

 from America, but, on the contrary, a most remarkable resemblance, 

 considering the great distance which intervenes between the re- 

 spective localities whence they come. Equally remarkable, as proving 

 the persistency of form and wide dispersion of these animals, is the 

 fact that whilst some forms are common to the relatively equivalent 

 Clinton and iSfiagara rocks of Canada, an equal number of these 

 jaws are identical with those from tho older Cincinnati group of 

 America, a formation generally regarded as the equivalent of the 

 Bala of this country. Even in the jaws which I regard as distinct 

 from the American forms, it will be seen, on comparing the ap- 

 pended description and figures with those of the former paper on the 

 subject, that the variations are but small in amount, and principally 

 depend on minor differences of form. As a rule, the dimensions of 

 the jaws, even of those of the same species, are less than in the 

 American examples, the largest English specimen met with not ex- 

 ceeding 2g lines in length, whilst some of the American forms are 

 3| lines long. 



In classifying these jaws I have adopted the same grouping as in 

 my former paper, not, however, without being thoroughly conscious 

 of its tentative character, as serving for paloeontological referenco 



Q. J. G. S. iN^o. 143. 2 c 



