136 The hish Naturalist. July, 



layers, and this may have resulted from the sinking of the 

 covering of mud thrown down upon the outstretched tentacles 

 after their decay, as suggested by Professor Sollas in explana- 

 tion of the appearance of Oldhamia radiata. 



The impressions of the tentacles in the principal specimen 

 are most distinct on a shining layer of the flags, which is 

 smooth and glossy, from a coating of minute spangles of mica. 

 This smooth surface would indicate a suspension of the deposit 

 of muddy sediment, and the continuance for a period of clear 

 water with quiet conditions. It would appear that in such 

 circumstances Monocraterion flourished, and spread abroad its 

 tentacles with the greater confidence. In other more clayey 

 layers the impressions of the rays are not so distinct. 



About an inch below the top layer (above referred to) 

 another mica-coated surface is spread out, and here the prints 

 of the tentacles again become more frequent and distinct. 



The size of the burrow in this genus, and its form, recall 

 Mr. Kinahan's genus Histioderma. But although in two cases 

 at the ends of the tentacles of Monocrataion there is an 

 appearance of forking, so many other of the rays show no 

 appearance whatever of dichotomy, but go straight out from 

 the burrow in a simple ray, that I assume the appearance in 

 these two cases is deceptive, and that there is no genetic 

 relation between this form and Histioderma. 



I have followed Torell in referring this form to the Worms » 

 but there are characters which point to other branches of the 

 Animal Kingdom, e.g., Ccelenterata. L,ess questionable Anne- 

 lid burrows and casts occur in the same layers with Mo?wcra- 

 terion. Between the rays and the burrows or lairs of 

 Mo?iocraterio7i, the pits and galleries of Arenicolites (Torell's 

 Diplocratcrion) are not uncommon, and more irregular worm 

 casts and trails are common. 



The above remarks do not give a complete answer to the 

 inquiry as to (< whether the internal tentacular markings run 

 up to the top of any given series of lateral and radial mark- 

 ings '* ; all that can be said is that they run up to the upper- 

 most series. Including the Swedish and Canadian forms, 

 Monocraterion ranges from the sandstones below the Paradoxidcs 

 beds to those which belong to the Olenitis zone. 

 Montreal* 



