INVEETEBEATE ANIMALS IIST PALEOZOIC EOCKS. 599 



castings of the Lobworm *. I am indebted to Lieut.-Col. Grant for 

 an extensive series of these markings, on which it can be seen that 

 the same trail often assumes very different characters, sometimes 

 resembling Crossochorda or Cruziana, and at others passing into the 

 ordinary Nereites or even into a simple trail. 



The Protichnites f of the Potsdam Sandstone are indubitable 

 tracks of Crustaceans ; yet it is possible, as I have shown in the case 

 of Limulus, that the same animals which produced Protichnites may 

 also have been the authors of the transversely ridged Glimactichnites 

 so often associated with them (figs. 4 and 5). It is also to be ob- 

 served that such forms as my Protichnites acadicus% or the Pr. 

 scoticus of Salter § form connecting links between this kind of track 

 and Cruziana. 



To the same category may be referred the trails with wave-like 

 transverse markings and no central line, found both in the Upper 

 Cambrian and Devonian, and which Whiteaves has named Gyrich- 

 nites\\. 



I copy here the remarks on JRusophycus (Bilobites) in my paper of 

 1873, merely adding that I now believe some markings of this kind 

 may have been produced by Chsetopod Worms, as well as by Phyl- 

 lopods : — 



" In a paper published in the ' Canadian I^aturalist,' 1864, 1 showed 

 that the singular bilobate markings with transverse striae, named 

 Rusoj)hycus by Hall, and found in the Chazy of Canada and the 

 Clinton group of New York, are really casts of burrows connected 

 with footprints, consisting of a double series of transverse markings, 

 and that a comparison of them with the trails and burrows of Li- 

 mulus justified the conclusion that they were produced by Trilobites. 

 I proposed for these, and for similar impressions of small size found 

 in the Carboniferous, the name given above. The Carboniferous 

 examples, I supposed, might have been produced by the species of 

 Phillijpsia found in these beds. A specimen recently obtained from 

 Horton shows this kind of impression passing in places into a kind 

 of Protichiiites, as if the creature possessed walking feet as well as 

 the lamellate swimming feet which it ordinarily used." 



I can scarcely doubt that the Cruziana semiplicata of Salter, and 

 O. similis of Billings from the Primordial of Newfoundland, must 

 have been produced by Crustaceans not dissimilar from those to which 

 Musichnites belongs. 



To Musichnites, rather than to Protichnites, ought perhaps to be 



* Luncls Univ. Arsskrift, vol. vi. p. 34, 1869. 



t Logan and Owen, Quart. Journ. Geol, Soc, vol. viii. 1852, pp. 199-225. 

 In the ' Geologist,' vol. v. 1862, pp. 128-139, and pp. 454-456, the proba- 

 bility of Glimactichnites having been the infallen gallery-tracks made by Para- 

 doxides burrowing in the sand of the old sea, like Sulcator and Kroyera (as 

 shown by Albany Hancock) burrow in the present sea-sands, has been suggested. 

 A similar explanation was given in Prof. Dana's ' Manual of Geology,' 1863, 

 p. 189. This does not, however, seem applicable to the Canadian specimens. 

 See figs. 4 & 5, and further on. 



\ Amer. Journ. Sci. ser. 3, vol. v. 1873, pp. 17,18, 23, fig. 2. 



§ Quart. Journ. Geol. Soc. vol. xii. p. 243, fig. 2. 



II ' Trans. Roy. Soc. Canada/ loc. cit. 



