444 Proceedings of Royal Society of Edinburgh. [sess. 
spines. Different modifications of such a type are not wanting, 
and an interesting series exists in E. striatus , E. hystrix, E. piri- 
formis , and E. antarcticus. The distinctive features of these are 
Fig. 2. — E. piriformis. 
Fig. 3. — E. liystrix. 
given in the foregoing table, together with the text-figure. The 
particulars regarding the first three forms are derived from the 
monograph of de Marval.* 
A consideration of the foregoing table and figures shows that 
E. antarcticus differs from each of the other species in more than 
one particular, and likewise has some points of agreement with 
each. I shall not recount the full details, but one or two points 
deserve further comment. While, as regards form, E. antarcticus 
* Tom. cit . , pp. 281, 308 , and 318. 
