304 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



Formation and Locality. — Upper portion of the Lower Cam- 

 brian, in the York formation: (8q)' calcareous shales 2 miles {^.2 

 kui. ) northzvest of the city of York, Pennsylvania, and eastzvard in 

 the same band of shales across York County to the Susquehanna 

 River. 



(i2w)' 2 miles (3.2 km.) north of the city of Lancaster, Pennsyl- 

 vania, near Fruitville, and westward at various localities to the 

 Susquehanna River, notably i mile (1.6 km.) north of Rohrerstown, 

 on the farm of Noah L. Getz. 



P^DEUMIAS, new genus 



{UaiSivfia = rudiment) 



The description of Pcedeumias is included in that of the genotype 

 P. transitans. I began by placing this form as a variety of Olenellus 

 thompsoni, but when I came to discuss its relations to Olenellus it 

 appeared desirable to give it a distinct generic and specific name, 

 as it is a transition stage between Mesonacis and Olenellus. 



Pcudeumias is a Mesonacis or an Olenellus with rudimentary 

 thoracic segments and pygidium posterior to the fifteenth segment, 

 as one may wish to consider it. The cephalon and first fourteen 

 segments are generically the same in the three genera. Their differ- 

 ences are in the dorsal shield posterior to the fourteenth segment. 



Mesonacis has a spine-bearing fifteenth segment [pi. 26] with ten 

 smaller but typical thoracic segments and a pygidium characterized 

 by postero-lateral spines. 



Pcedeumias has the fourteenth segment as a median spine posterior 

 to which there are from two to six rudimentary segments, and a 

 .rudimentary pygidium [pi. 33]. 



Olenellus has the fifteenth segment as a terminal telson without 

 segments or pygidium posterior to it. 



Genotype. — Pcedeumias transitans Walcott. 



Stratigraphic range. — Lower Cambrian (Georgian) terrane, in 

 upper portion, in association with Olenellus thompsoni. 



Geographic distribution. — Typical locality Georgia, Franklin 

 County, Vermont. It has been found on the south side of the St. 

 Lawrence River at Bic, in the Province of Quebec; at Bonne Bay, 

 in northwestern Newfoundland ; in Labrador, at L'Anse au Loup, 

 on the Straits of Belle Isle ; south of Vermont, in Lancaster and 

 York cotmties, Pennsylvania ; near Cleveland, in eastern Tennessee ; 

 and in Shelby County, Alabama. 



' Collected by Prof. Atreus Wanner. 

 ' Collected by Prof. H. Justin Roddy. 



