FOSSILS OF BELT TERRANE 237 



from the lower Cambrian slates of Greenwich, New York* It differs 

 little from that species ; but it is not probable that the same species of 

 annelid existed at the two distinct geological horizons and on opposite 

 sides of the continent. 



Formation and locality yielding Planolites corrugatus. — Algonkian, Grey- 

 son shales ; Sawmill can,yon, 4 miles above Neihart, Montana. 



Planolites superhus, n. sp. 



(Plate 24, figure 9.) 



The cast of a large burrowing worm occurring in a sandy shale inter- 

 bedded in the Beltina danai shales of Sawmill canyon. This burrow 

 indicated the presence of a large annelid that may be compared with 

 some of those that made almost similar burrows in the arenaceous muds 

 of lower Cambrian time and in part throughout geological time from the 

 Belt terrane to the sediments now gathering in seas and lakes. The cast 

 of the burrow extended for some distance in the bed in which it occurred, 

 and several less well preserved specimens were seen near it. 



Formation and locality yielding Planolites superhus. — Algonkian, Grey- 

 son shales ; Sawmill canyon, 4 miles above Neihart, Montana. 



Crustacea. — The crustacean remains are in a most unsatisfactory con- 

 dition of preservation, but they give evidence of the presence of types 

 closely related to the Merostomes that may be represented by more than 

 one genus and several species. I have suspected the presence of a large 

 phyllopod, but have no satisfactory evidence of its presence. 



When preparing the note on the "Affinities of the Trilobita," pub- 

 lished in 1881,t the class Poecilopoda was divided into two subclasses, 

 Merostomata and Palseadse; the former included the orders Xiphosura 

 and Eurypterida, and the subclass Palseadse including the order Trilobita. 

 Subsequent discoveries have led some naturalists to bring more closely 

 together the Trilobita and the Phylloj^oda; but the discovery of represent- 

 atives of the Merostomata in pre-Cambrian rocks appears to strengthen 

 the view that the Trilobita and the Merostomata are branches of a com- 

 mon line of descent, or that the Trilobita are an offshoot of the main 

 branch represented by the Merostomata. The Phyllopoda and Merosto- 

 mata may have developed before the Trilobita. 



The discussion of this and a number of other, questions raised by the 

 presence of such highly organized crustaceans in pre-Cambrian rocks is 

 deferred with the hope that another season's field-work will afford more 



* Tenth Annual Report, U. S. Geol. Survey, 1891, pi. 60, fig. 5. 

 jBull. Mus. Comp. Zool., vol. viii, 1881, pp. 208-211. 



