4M 



I'liOCKKDINUS OK THE 0EOI,O(}I(AI, HOriT.TT. 



May 1 1 , 



3. Are Proti(hi\it»H awf C'liniiifticliTiitcs the trnch of Tn/ohife»? 



In his (Irsorifilioii of /'rotidnites, Prof. ()"en Hays :— " Tlic 

 LlnmlvH, -vvliicli hfis the siiir.ll anterior j)air ol' limbs (wnr th(^ 

 niiddlo lino) uul Iho next four lateral jjairs of linilm hifurcatf 

 at tlu; fret' extremity, the last ■ pair of latt'i.il linihs with lour 

 iura<'llil'orm apjiendupeH, and a long slender hard tail, <;ome8 the 

 nearest to my idea of the kind of anijnal \vliieh has left the im])res- 

 Bions on the Potsdam sandstone''*. In 1M(;2, J)r. .1. VV. Dawsou 

 lusted this opinion hy actual experiment, on a sandy beach near (ho 

 mouth of the Scarhoronph river, on tlio coast of Maine. Having 

 eauglit a LhnvhiS he kept it nlivc for seVJTal days, and " tried its 

 m''>do v»f locomotion under various couditions on the sandy shore, and 

 presei-ved sketches of the markings "t. His figures and descriptions 

 prove dearly that the track;? on the sandstone could have lu'in made 

 by an animal having a structure like that oi Llmnlvr.. The grooves 

 along th(; sitlo of the track vere made by the (>dge8 of tlu* broad 

 teplialothorax, the small pit-like impressions by the extremitits 

 of the larg<' limbs, the transverse grooves by the lanielliform feet, 

 and the median groove by the telson. If it be grant( il ihnt^lsaji/ms, 

 in addition to its thoracic legs, possessed a set of lamellar .^wimming- 

 appcndages under the pygidium, then Uie struetuns ofthonnder- 

 surfuce would be sufficiently like that of Lhnu/us to enable it to 

 l)roduce the same markings. The median groove m'., be made by 

 a Trilobite Avith a caudal s])ine like that of Meiiahiapis hi ros ( A ngelin ). 

 This species is a irxn} A-sophus. The large Trilobite of the I'otschim 

 sandstone, Dikehnephahiiii, differs littli- in general structure from 

 Atifiphns, while the ])ygidium of several of the species evin(>es a ten- 

 dency to become spinous around the margin. The genus A'jlii!>jtis 

 (Hall) ap])ears to me to be a Tiilobite of the same group; and, more- 

 over, the specimens iigured seem to lie the tail ind not the head. 

 Wliat are 8npp(»sed to be the t^yes are the bases of two spines, like 

 the one that occurs on the pygidium oi Buthyurus sjHniyer (Ackhis- 

 pis spinlitef, Hall). 



Dr. Dawson, after comparing all the facts, says: — "On the whole 

 we may safely coiiclude that, if any of the larger primordial Trilobites 

 wore provided with walking- and swimming-leet of the type of 

 those of Linndns, but differing in tletails of structure, they may have 

 produci^l both the Protlchnltct, and tlu! Cihnarfichnites.'" Prof. 

 J. I). Dana, also speaking of the latter, says; — "It has been re- 

 garded as the track of a very largo (iasteropod ; but it is (juite as 

 probable that it was made by the clusters of foliaceous aj)pendageH 

 of one of the great Trilobites — these a])pendages being its locomotive 

 organs''^. Tho following, therefore is the present state cf the ques- 

 tion : — 



1. The tracks cotild have been made cither by a rjmvh(s or by a 

 Trilobite. 



* Quart. Jonrn. Geol. Soc. vol. viii. p. 224. 



+ t'liimdian Nuturalist and Geologist, vol. vii. p. 27(3. 



I Manual of Geology, p. 18."). 



