COEEESrONDENCE. 



455 



ing fossil surface-markings, my friend Dr. J. W. Davrson, of Montreal, 

 must have been engaged in the useful labour of preserving faithful re- 

 cords of the track-marks of Limulus poli/phemus on the sands of Orchard 

 Beach (Grulf of St. Lawrence), for the purpose of coin])aring them with 

 the fossil tracks, termed Prollchnites and Cllmaciichni tcs, found in the 

 Potsdam sandstone of Canada. 



The results of these well-directed researches have been described and 

 illustrated by Dr. Dawson in the Canadian 'Naturalist and Geologist' 

 for August, 1802 (vol. vii. No. 4), p. 271, etc. ; and it ;i])])(vir.s certain that 

 the trail of Limulus on w^et sand is very similar io V vollcliaHoH, except- 

 ing that the latter has not the lateral furrows that are produced in the 

 former by the edges of the carapace. Swimming in very shallow water, 

 Limulas produces on the sand a trail very similar to CUmactichni tes ; the 

 latter, however, showing lateral and median ridges, whilst the former has 

 furrows instead. 



Dr. Dawson agrees, therefore, with Professor Owen in referring the 

 Protichnitcs to a Limuloid animal ; and is strongly inclined to refer Cli- 

 mactichnites to the same agent. Still he thinks it not impossible that the 

 large Lower Silurian Trilobite, Paradoxides, may have been the animal 

 that produced all the marks in question. 



With the fact before him, that Clima'ctichnital markings are left on a 

 subaquatic surface by Limulus, Dr. Dawson, of course, rejects the hypothe- 

 sis of ClimacticJmites being gallery-tracks, as advanced in my paper above 

 referred to Hoc. cit. p. 139). Still these recent tracks differ from what 

 Dr. Dawson regards as their primaeval analogues, in that their " lateral and 

 medial lines arc furrows instead of ridges ;" and therefore the identifica- 

 tion is not complete. I would ask that the question still remain open until 

 Dr. Dawson and other good naturalists have more material at hand and a 

 M ider basis for conclusions. 



" I may add that the burrowing of Limulics poh/phcmus,'" Dr. Dawson re- 

 marks, "is easily effected in soft sand, but is confined to a mere bmyiug of 

 itself beneath a very slight smooth elevation." The great well-known 

 North American Trilobites {Paradoxides), however, whose bodies exactly 

 fit in width to the Climactichnital and Protichnilal trails of Canada, and 

 ■whose abiding place was really the muddy sea-bed on the geological hori- 

 zon of the Potsdam sandstone, in all probability crawled over these littoral 

 sands, just as the LJmulus frequents the existing sandy beaches in spring 

 and summer; and (like Sulcator and I^roeijera, loc. cit. pp. 131, 138, 139) 

 it may have burrowed in them, with much longer burrows than Limulus 

 makes, and in that case the in-fallen galleries would supply the raised 

 ridges of the Climactichnite. 



AVe need not suppose the presence of Limulus, or of any unknown 

 Limuloid aninuil, in the primordial sea; for there is little doubt, if any, 

 that Paradoxides, known to have then existed, can have made the trails 

 in question (as Dr. Dawson allo\A s, p. 277), if they had the usual crusta- 

 cean lo('onloti^'e apparatus ; and "it seems almost certain, from aualog}^ 

 that lli(>y must have possessed such organs" (Dawson, loc. cit. p. 277). 

 Nor does the trail of correspond exactly with the fossil tracks; 



the edges of its carapace produce, in cra^^ling, sid(>-furrows not seen in 

 Protichniies ; and its subacjuatic trail has but a general resemblance to 

 Cli marl ichni tcs, as far as we can learn from tlie published observations. 



Dr. Dawson, in his interesting paper before nu\ also iu)tices (p. 275) (ho 

 occurrence, at Orchard IJcach, of " small Climactichnile-like tracks" that 

 were made, as he ascertained, by a large beetle [Melolonfha ( Pol >/pI/j/lla) 

 variolosa?), "which oceusionally settled on (he wet saud and crept tor 



