884 



Pig. 358. 



Pig. 360. 



Pig. 359. 



Pig. 361. 



Fig. 358. — Pragment of R. calciferus, showing the inner surface of the ectorhin with the 

 stclong remaining, but all other parts worn away. 



Fig. 359. — A cast of R. Oweni, showing the impression of the inner surface of the ector- 

 hin. 



Fig. 360. — Tetragonis Murchisonii (Eichwald) reduced. 



Fig. 361. — A portion of 360, natural size. 



Fig. 360 is a reduced outline of Tetragonis Murchisonii, from Eicli- 

 wald's ' Urwelt Russlands,' pi. iii. fig. 18. It does not show all the lines 

 given in the original figure, as they could not well be represented on so 

 small a scale. Fig. 361 is the upper part of the same figure, of the size 

 of the original. The vertical lines are the impressions of the radial sto- 

 lons, and the finer transverse lines the grooves of the cyclical stolons. 

 By comparing fig. 359, it will be seen that the grooves in both figures 

 have precisely the same arrangement ; that is to say, the dark points, 

 representing the openings of the cylindrical cavities, once occupied by 

 the tubes, occur at each alternate crossing of the grooves. It would 

 appear, therefore, that Eichwald's genus Tetragonis was founded on a 

 species of Meceptacidites, with the ectorhin removed. The genus Ischa- 

 dites also exhibits very similar markings, as may be seen by comparing 

 the figures of/. Kmnigii (Murch.), on pi. 12, ' Siluria,' and the follow- 

 ing of R. Canadensis. 



The specimen represented by fig. 362 has been figured by me in the 

 Geology of Canada, p. 309, under the name of Isehadites Canadensis. 

 It is the cast of the inner surface of the ectorhin, and differs remarkably 



