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MONOCRATKRION AND OU3HAMIA. 



BY G. F- MATTHEW. 

 (Geological Survey of Canada.) 



Sinck Professor Cole has mentioned with commendation my 

 work upon the Cambrian genera Monocratcrion and Frcena, in 

 an article on Oldhamia and Histioderma in the Itish Naturalist 

 for April, 1901, and implies a desire for further knowledge of 

 the former genus, I have re-examined the specimens of Mono- 

 craterion in view of his comment on the course and nature of 

 the ray-impressions. The " impression of the supposed 

 tentacles" can be traced only along the more open, and 

 trumpet-shaped part, of the burrow of the animal, and they 

 disappear where the walls of the burrow begin to descend 

 rapidly, and from that down the sides are smooth. 



As may be concluded from Torell's description of Micrapium^ 

 that form had a mound at the burrow, and this is the case also 

 with the Canadian form oi Mono craterion, only the mound has 

 no connection with the slopes outside the burrow. When the 

 summit of this mound is abraded, it is seen to consist of several 

 superimposed layers like the coats of an onion. This cone 

 had no connection with the sides of the burrow, as the tenta- 

 cular markings and the smooth surface of sand on which the 

 animal rested run out from beneath it. It appears not to have 

 been a portion of layers thrown down upon the animal after 

 death, as a shaly mud of different texture separates it from the 

 overlying shale. We can only suppose that it was some sort 

 of a protective coating, such as the caddis-worms, or some of 

 the marine worms, build to protect the soft body. 



Around the central mound, and resting partly on it, but 

 chiefly on the flatter expanded part of the trumpet-shaped 

 opening of the burrow, is a ring of .mud or shale, part of a 

 superior layer that covered the mound at the centre of the 

 burrow and the prints of the tentacular rays. We may sup- 

 pose that the mud bed that covered over this organism and its 

 burrow sank down around the mound as the softer parts of the 

 animal decayed, and left the depressed ring of shale which we 

 now find surrounding the cone of the burrow. The prints of 

 the tentacular rays are depressed on the upper surface of the 



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