36 C. D. Walcott — Position of the Olenellus Fauna. 



of New York. K.pannula ranges from the Olenellus zone to 

 the Middle Cambrian, in Nevada, and is found in the upper 

 portion of the Olenellus zone in New York. 



Linnarssonia sagittalis var. Taconica is scarcely to be con 

 sidered a typical Olenellus zone species, as it occurs so high in 

 the Lower Cambrian section. Still, as it is associated with 

 Olenellus we may consider it as forming a part of the fauna,, 

 and compare it directly with the same species as found in the 

 Paradoxides zone of New Brunswick and Sweden. Of the six 

 species of the genus Obolella none are known to occur in the 

 Middle Cambrian, and it is not until we reach the Upper Cam- 

 brian that we find representatives of the genus. The genus 

 Orthis, as represented by 0. Salemensis and 0. Highlandensis 

 (the broad and narrow hinge types), is not known to occur in 

 the Middle Cambrian zone, although both forms of the genus 

 are represented in the Ordovician. Among the species re- 

 ferred to Orthisina, we find that 0. orientcclis is very closely 

 related to 0. pepina of the Upper Cambrian, also that 0. festi- 

 nata is of the type of O. exporecta of the Paradoxides zone of 

 Sweden and Orthis JBillingsi of the New Brunswick Middle 

 Cambrian. Camerella antiquata and C. minor have no repre- 

 sentatives in the Middle or Upper Cambrian. 



As a whole, the Brachiopocla are strongly represented in the 

 Lower Cambrian and do not exhibit any special evidence of 

 embryonic character when compared with the fauna of the 

 Middle and Upper Cambrian. 



Lamellibranchiata. — The genus Fordilla and the form de- 

 scribed as Modioloides jprisca appear to be the representatives 

 of the Lamellibranchiata in the Olenellus zone. The presence 

 of these two shells is of unusual interest, as none of the same 

 class are met with in the geologic succession before the abrupt 

 appearance of the group of species in the Arenig (Lower Ordo- 

 vician) strata of South Wales. 



Gasteropoda. — Among the Gasteropoda, the genus Scenella 

 is represented in the Upper Cambrian by simple patelloid 

 shells. It has not been found in the Paradoxides fauna of the 

 Atlantic basin, but in the Middle Cambrian strata of the Mt. 

 Stephen section in the Rocky Mountains a representative 

 species was found by Dr. Rominger. The forms referred to 

 the genus Stenotheca are very closely allied if not identical in 

 the Lower and Middle Cambrian zones. 8. rugosa, of the 

 Lower Cambrian, and S. Acadica of the Paradoxides zone are 

 examples of this intimate specific relationship. The little Pla- 

 tyceras of the Lower Cambrian has a representative in the form 

 described by Dr. C. Rominger from the Mt. Stephen Middle 

 Cambrian of British Columbia. A single species in the Upper 

 Cambrian connects this genus with the Ordovician fauna. Pleu- 



