446 



MERISTIC VARIATION. 



[part I. 



(387. Amblypneustes (S. Australia): 6-rayed specimen [no description or statement 

 as to symmetry]. Haacke, W., Zool. Anz., 1885, p. 505. (See No. 679.) 



(4) Cases of imperfect reduplication of a radius. 



'688. Amblypneustes griseus : having one of the ambulacra doubled 

 (Fig. 139); the apical system was normal. The width of the anterior 

 ambulacral region was almost double that of the others : it contained 

 two ambulacra lying side by side, each, as usual, composed of a double 

 row of plates with an ambulacral area and two poriferous zones. The 



is.aPca 





Fig. 139. Amblypneustes griseus, No. 688. Specimen having the anterior 

 ambulacrum doubled. I. The test seen from the apex. II. Details of anterior 

 ambulacrum shewing combined poriferous zones between A and A. The dotted line 

 bisects the ambulacrum of double width. (After Stewart.) 



areas and external poriferous zones are like those of a normal ambula- 

 crum ; but the poriferous zones which touch one another are fused 

 together, with the pores irregularly arranged. The combined porifer- 

 ous zones are not quite equal to the sum of two normal ones. The 

 whole of this area, formed of the union of two ambulacra, projects as a 

 ridge which is continued down the whole of the side of the shell. 

 Stewart, C, Jour. Linn. Soc, xv. p. 130, PI. 



689. Hemiaster latigrunda : right posterior ambulacrum double, the 

 two resulting ambulacra are closely adjacent peripherally and a small 

 interambulacral area is formed between them in their more central 

 parts. There are 6 oculars but no extra genital. Gauthier, /. c, tigs. 

 5 and 5 bis. 



690. Hemiaster batnensis : right anterior ambulacrum double, the 

 two ambulacra are in contact through all their length. Cotteau, Pal. 



frarig., 1869, p. 150, PI. xx., and Gauthier, I. c. 



[For interesting evidence as to variation in the number of genital pores on the 

 costals in several genera of Echini, see Lambert, Bull. Soc. Yonne, 1890, xliv. Sci. 



