library! 



V« 





THE OTTAWA fiATURALIST. 



Vol. XIII. 



OTTAWA, DECEMBER, 1899. 



No. 9. 



NOTE ON AN ECHINODERM COLLECTED BY DR. AMI 

 AT BESSERERS, OTTAWA RIVER, IN THE PLEIS- 

 TOCENE (LEDA CLAY). 



By Sir J. William Dawson, C.M.G., LL.D.,^F.R.S. 



The specimen is a flattened disc, about three centimetres in 

 diameter, in a circular nodule split open. The central part shows 

 inclined bars or tubercules and remains of slender spines which also 

 fring-e the margins pointing mainly in one direction (backward). 

 There are indications of a shallow sinus in front. The spines are 

 flattened, and pointed, and show traces of an echinoid cellular 

 structure. 



The specimen is probably the flattened test and spines of a 

 spatangoid sea-urchin, which has burrowed in the clay when soft 

 and has been buried up and compressed owing to its not having 

 been penetrated with earthy matter. This mode of preservation 

 renders it impossible to see distinctly the markings on the shell, 

 which are obliterated by flattening or covered with the remains of 

 the spines, making the determmation of the genus and species 

 ver}' unsatisfactory. 



It may belong to either of the genera Spatangus, Brissus, or 

 A/hphidotus, as defined by Forbes for the European species. Look- 

 ing for it among existing species, I do not know any of this type 

 on our coast, except that Brissus lynfer is said to have been 

 dredged by Goodsir in Davis Straits; but the present specimen 

 does not seem to agree in form with that species. On the east 

 side of the Atlantic, Spatangus purpureus extends to Norway, and 

 so does the common Amphidotus coidatus. Sars, in his memoir on 



