446 



M ERISTIC VARIATION. 



[part I. 



687. 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 







s ^Al 



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, I. c, tigs. 

 5 and 5 bis. 



690. Hemiaster batnensis : right anterior ambulacrum double, the 

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



franq., 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. 



