652 



MESSRS. RITCHIE AND MCINTOSH ON 



[June 16, 



functionless. It is moreover the nearest to the centre of the 

 plate, whereas the median pore-pair should lie in the outermost 

 row. Series h contains two abnormal plates, twenty-nine and 



Text-fig. 140. 



III. 



Abuoemalities in Ambtjlaceai Areas op EcJdnus esculentus. 

 (For explanation of the lettering see text-fig. 138.) 



thirty, each composed of two pore-plates. The absence of distinct 

 sutures in the first renders identification of plates impossible, but 

 the second is composed of an adoral primary and an aboral demi- 

 plate. Thirty is an intercalated plate having no corresponding 

 individual in the adjoining ambulacral series. 



Series a of area IV (text-fig. 141) contains but one abnormal 

 plate, thirty, which is composed of four primitive plates, three of 

 which appear to be primaries, only that preceding the aboral being 

 unmistakably a demi-plate. Of the four the adoral is imperforate. 

 In series b, twenty-nine is composed of an adoral primarj' succeeded 

 by a demi-plate ; thiity, of two primaries, the adoi-al without 



Text-fig. 141. 



Abnoemahties in'Ambuiaceal Aeeas oe EcJiimts esculentus. 

 (For explanation of the lettering see text-fig. 138.) 



pores ; thirty-one, of a single huge primary ; thirty-one a, of a 

 separate demi-plate, perhajss an isolated portion of thirty-one ; 

 and thirty-two, of three plates, the adoral a lai'ge primary, the 

 other two, small demi-plates cru.shed into the upper corner of the 

 compound plate. Thirty is an intercalated plate with no corre- 

 sponding individual in the adjacent row. Thirty-eight is also 

 unusual, being composed of five elements, the adoral and median 

 of which are primaries, while the remainder are demi-plates. 



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