28 SMITHSONIAN MISCELLANliOUS COLLECTIONS VOL. 57 



the cephalo-thorax it has a nearly transverse posterior margin with 

 shghtly rounded lateral angles. The anterior outline is curved so 

 as to give an inward slope to the sides and a rounded, slightly trans- 

 verse section along the central portion. No traces of eyes. I am 

 strongly inclined to the view that the part preserved is the large 

 epistoma characteristic of the family Sidneyidae. 



Abdomen. — There are traces of seven abdominal segments. In 

 front of the epistoma? is the remnant of a segment which was largely 

 broken away in exposing the epistoma?. The same is true of the 

 anterior of the segments united in the abdomen ; of this segment 

 only a small fragment remains on the left side. The first fairly 

 well preserved segment has a length of 13 mm. and a width of 30 

 mm. Before the anterior margin was removed it had a length of 

 16 mm. The next two segments are large and broad, and the last 

 two narrow and long. All are more or less pushed one over the 

 other so as to obscure their true proportions. 



Surface. — The surface of all parts of the abdomen is ornamented 

 by irregular, imbricating lines, roughly sub-parallel to the longi- 

 tudinal axis of the abdomen, or else, toward the outer edges, sub- 

 parallel to the gently curved outer margins of the segments. The 

 epistoma ? has much finer lines sub-parallel to its lateral margins. 



Observations. — The outline of the body of this species suggests 

 the form of Pterygotus hilobus Salter var. inornatus Woodward.' 

 The surface markings are unlike those of Pterogotus, Eurypterus, 

 and other genera of the Eurypterida, as are also the proportions of 

 the abdominal segments. 



Formation and locality. — Middle Cambrian : Stephen formation, 

 Ogygopsis shale, west slope of ridge between Mount Field and 

 Mount Wapta, about 3800 feet above Field on the line of the 

 Canadian Pacific Railway, British Columbia, Canada. 



A second species of this genus or a closely allied form occurs in 

 the Redlichia chinensis zone of Indo-China. (See p. 19.) It is the 

 oldest Merostome now known as it comes from the horizon of the 

 Man-t'o shale formation of the upper Lower Cambrian terrane.^ 



^ Monogr. British Fossil Crustacea, Order Merostomata; 1866-1878, pi. 10. 

 ^ See Willis and Blackwelder, Research in China, 1907, Vol. i, Pt. i, p. 26. 



