1867.] SALTEE TKACE.S OF PTERASPIS. 333 



It is, however, until better specimens attest its true relationships, 

 placed with fusea in the group Conidus, which (according to Messrs. 

 Adams, Gen. ii. p. 116) is a subgenus of Zonites. 



" It is probable that there is a third species among the fragments 

 which have been found ; presenting a shape more resembhng the 

 H. conulus, and other trochiform snails. It would be premature, 

 however, to venture on a description until more perfect specimens 

 have been obtained." 



3. On some Tracks of Pteeaspis(?) in the Uppee Ludlow Saxdsto^^e. 



By J. W. Salter, Esq., P.G.S., A.L.S. 

 The Society has always received with patience communications 

 tending to explain those surface-markings on our beds of rock which 

 may be referred to the movements of animals. In many cases, 

 indeed, these are the only proofs left us of the existence of certain 

 types ; while in others the remains of the animals themselves have 

 been discovered after we had learned to guess at their nature from 

 the impressions they had left behind them. 



There is an obvious reason for the more certain preservation of 

 the track than of the animal which made it, when such imprints have 

 been made upon the sea-shore ; for the impressions have generally 

 been made between tide-marks, their preservation being due to the 

 covering up of the imprinted layer by another upon the return of the 

 tide. It is certain, then, that this portion of the stratum must, in 

 general, be unfit for the preservation of the animal itself, even if it 

 were not expecting too much 'to find it dead where we have the best 

 proof of its having been alive and in the enjoyment of its functions. 

 The wash of the tide, throwing up as it does dead shells, and hard 

 parts of the crust of jointed^animals, is very destructive even of these ; 

 and the majority of waifs upon the shore are decomposed and 

 destroyed by the atmosphere soon after they are thi^own beyond the 

 reach of ordinary tides, and before there is a chance of sufficient sedi- 

 ment being accumulated to resist the next incursion of the waves. 

 In deeper water the relics are abundant, but the tracks are, of ne- 

 cessity, rare. 



We may take for an instance the fine cliff of Caradoc or Bala 

 sandstones, which is so well kno-svn, at Aberystwith. Here ripple- 

 marks and tracks and trails are copious enough, but not a fossil has 

 been detected. The Coal-measure cliffs at Waterwinch near Tenby 

 furnish another example. In the Lingula-flags, too, we find whole 

 surfaces scored by the Hymenocaris, without a fragment of the artist 

 who engraved them ; and every collector of fossils knows that he 

 need not, as a rule, expect to find good fossils where tracks abound. 



The Downton or Upper Ludlow sandstones of Kington, on the 

 borders of Herefordshire, are unquestionably a shallow- water, and 

 in part a shore deposit. The irregular silty character of the bed 

 itself, the disjointed fragments of crustaceans and fish, the numerous 

 vegetable fragmeuts, the scarcity of shells (for even Linguloe are 

 rare), attest this. And we know from other evidence that the close 



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