56 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



The presence of so highly organized a medusa in the central part 

 of the Middle Cambrian terrane is not surprising in view of the num- 

 erous traces of Medusae in strata of Lower Cambrian age. 



Genotype. — Peytoia nathorsti, new species. 



Stratigraphic range. — Limited to a stratum of dark siliceous shale 

 2 feet in thickness in the lower portion of the Ogygopsis zone 

 ( = Burgess shale) of the Stephen formation as described in 1908. 

 (See footnote on page 51 of this paper.) 



Geographic distribution. — On the west slope of the ridge between 

 Wapta Peak and Mount Field, north of Burgess Pass, and about 

 3800 feet above Field on the line of the Canadian Pacific Railway, 

 British Columbia, Canada. 



PEYTOIA NATHORSTI, new species 



Plate 8, figs. I and 2. 



Of this medusa we have three specimens of the impression made 

 by the subumbrella lobes. The flattened disk has a broadly elliptical 

 outline with the outer margin slightly indented where the outward 

 curving ends of the lobes unite so as to indicate very short, rounded 

 lappets. 



There are thirty-two lobes arranged in a quadrate series. This 

 includes four large lobes, one extending outward on each side of the 

 quadrate central opening, and seven narrow lobes between the broad 

 lobes in each quadrant. The inner ends of the lobes terminate so as 

 to form a quadrate opening with one of the broad lobes at the center 

 of each side. Each lobe has two short, broad points that project 

 inward a short distance. These points appear to have been the points 

 of attachment of the parts about the mouth, or possibly oral arms. 



No traces of a concentric muscle band. 



A few radial lines parallel to the margins of the lobes serve to 

 define a narrow band on each side of each lobe. A trace of the canal 

 system of the subumbrella is shown by the cast of small anastomosing 

 canals extending out on some of the radial lobes to the outer margin. 



Dimensions. — The largest disk has a diameter of 63 mm. on its 

 longer axis, and 51 mm. on the shorter. The central quadrate open- 

 ing is 21 by 17 mm., exclusive of the projecting points. 



Observations. — The three specimens of this species occur in part- 

 ings of the siliceous shale in association with annelids and crustaceans 

 that indicate that they were deposited on the bottom in quiet water, 

 and were not left on a beach between tides. The subumbrella disk 



