252 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Clearly the ambulacral areas have suffered reduction here as well as the 
inter-ambulacral, and the extent of reduction in the two types of area is 
roughly proportional, the diameter relationship between the ambulacral 
and inter-ambulacral areas of the normal specimen being as 1 to 1*783, and 
of the six-rayed specimen as 1 to 1*737. The proportionally greater loss 
in diameter of the inter-ambulacra is obviously too small to support 
Jackson’s statement. 
EXPLANATION OF PLATE. 
Eoman and Arabic numbers mark the ambulacral and inter-ambulacral areas 
according to Loven’s notation. 
Eig. 1. Incomplete development in Echinus esculentus . Moray Firth specimen 
viewed from flattened, abnormal aspect, showdng the termination of imperfect 
ambulacrum V., the very numerous and irregular regulation plates or “space-fillers” 
in the corona, and the asymmetrical position and abnormal plates of the apical 
area. x 2. m = madreporite. 
Fig. 2. Hexamery in Echinus esculentus. Apical aspect of Moray Firth specimen. 
Natural size. 
(Issued separately September 4 , 1914 .) 
