Geology. 417 



except on the dry sand above high-water mark. The creatures are 

 driven on shore only in storms, and then, owing to the lightness of their 

 crusts, are drifted high on the beach. The remains are probably to be 

 found in circumstances favorable to their preservation, only on the muddy 

 bottoms at a distance from the sandy shore. Young individuals appear 

 to frequent the sand only in summer, and occasionally to be imbedded 



(6.) If we inquire what animals, known to paleontologists, have pro- 

 duced the Protichnites, it would seem tljat no others fulfill the necessary 

 conditions in any particular, except the larger trilobites, for instance those 

 of the genus Parudoxides. It is true that we know nothing as yet of 

 the feet of these creatures, but it seems almost certain from analogy that 

 they must have possessed such organs. Nor have these trilobites a caudal 

 spine like that of Liraulus; but here again Mr. Billings points out to mo 

 that the pygidium of Paradoxides is narrow and spine-like, though I 

 should think not sufficiently so to form the very distinct median groove 

 of Protichnites, unless indeed the animal was in the habit of walking 

 with this organ pointed downward. On the whole we may safely conclude 

 that if any of the larger Primordial trilobites were provided with walking 

 and swimming feet of the type of those of Liraulus, but differing in de- 

 tails of structure, they may have produced both the Protichnites^and the 

 Climactichnites. On the other hand, it is quite probable that these im- 

 pressions have been formed by Crustaceans yet undiscovered, and ap- 

 proaching in some respects more nearly to Limulus than any of the 

 known trilobites. In this last case I should suppose that the animal in 

 question had a flatter or more shallow cephalo-thorax than that of Lim- 

 ulus, proportionately stronger and perhaps more divided feet, and a stouter 

 caudal spine. 



It is scarcely necessary to observe that the footprints of Liraulus diflFer 

 materially from those of the higher Crustaceans, and also from the gal- 

 leries formed by many small burrowing Crustaceans. AVith these last Mr. 

 T. Rupert Jones, in an interesting article in the " Geologist" for April, 

 seems disposed to compare Climactichniles Wilsonii ; but tliis appears to 

 nie to have more the character of a surface impression, though what 

 appear to be galleries of small Crustaceans are also found in the Potsdam 

 sandstone, the 'Nereites' of Emmons,* from theTaconic rocks of that 

 author, also resemf)le in some respects the sub-aquatic trails of Limulus, 

 and may be the work of Trilobites; and the same remark applies to 

 some of the markings from the Clinton of New York, figured by Hall,t 

 and referred to Crustaceans aud worms." 



Rote. — It appears very improbable that the fossil Paradoxides, like 

 other Trilobites, would be so uniformly deprived of stout limbs, if the 

 Hving animal had them ; for limbs that could make the very large tracks 

 of the Protichnites, would hardly fail to become fossilized. The refer- 

 ence of the Chimactichnites tracks to the Paradoxides is in all probability 

 right. The same opinion is expressed by the writer in his Manual of 

 Geology in a paragraph printed six months since, though the work is but 

 just now leaving the press. •'• °- ^' 



