I 



NO. 2 MIDDLE CAMBRIAN HOLOTHURIANS AND MEDUS.E 55 



MACKENZIA COSTALIS, new species 



Plate 13, figs. 2 and 3. 



Body elongate, cylindrical, and contracting at each end. Marked 

 by from eig^it to ten longitudinal bands that are outlined by narrow, 

 slightly elevated lines as shown in fig. 3, pi. 13. The anterior end has 

 a ring of what appear to be narrow plates surrounding a central 

 opening. The interpretation of the ring is that it formerly sur- 

 rounded the oesophagus near its outer end and that the outer margin 

 of the oesophagus with the tentacles has been removed. The posterior 

 end is contracted slightly. No trace of the anal opening has been 

 seen. 



Surface smooth so far as determined. 



Two specimens have been found and photographs of both are re- 

 produced (natural size) by figs. 2 and 3, pi. 13. 



As mentioned under the genus, the body of this species has the 

 general form of the body of Synaptula hydriformis (Lesseur). 



No traces of calcareous deposits have been observed, except possi- 

 bly in the ring about the anterior end. In this the calcareous matter, 

 if it was originally present, has been removed. My present im- 

 pression is that nearly all calcareous matter was removed by solution 

 in the mud deposit prior to its consolidation and alteration into 

 rock. 



Formation and locality. — Middle Cambrian: (35k) Burgess shale 

 of the Stephen formation ; west slope of ridge between Mount Field 

 and Wapta Peak, one mile northeast of Burgess Pass, above Field on 

 the Canadian Pacific Railway, British Columbia, Canada. 



SCYPHOMEDUS^E 



Order RHIZOSTOM^ 



Family Undetermined 



Genus PEYTOIA, new genus 



All that is known of this genus is given under the description of 

 the species P. nathorsti. 



The relation of the genus to the Order Rhizostomae is shown by its 



(a) Discoidal bell without known annular furrow or pedalia, 



(b) Margin of bell cleft into lappets, 



(c) Absence of tentacles, and 



(d) Mouth probably with adradial arm-like processes. 



