THE AMBULACRA. f,!i 



All these markings, whether on the deltoids, side plates, or lancet-plate, are merely 

 a delicate surface ornamentation, as was pointed out by one of us in i s s ] i. 

 According to Hambacli -*, however, "Likewise is the zigzag plated integumen! pre- 

 served which covers the ambulacral field, incredible as this may sen, to Mr. Carpenter, 



whose incredulity, however, is no evidence to the contrary The ambulacra] 



field which is marked e in Roemer's fig. 2 on plate i. of his ' Monographie der Blas- 

 toideen' indicates the existence of a layer or integument covering the Bame (although 

 not described as such)." The figure in question represents an ambulacrum which is 

 very much in the condition of those shown in our PI. I. figs. 10 & 11 ; and we cannol 

 at all see how it indicates the existence of any covering integument. The cross 

 markings on the ambulacrum are the lateral branches of the food-groove, which are 

 continued outwards over the sutures between the side plates, and we quite think that 

 Roemer was right in omitting to describe them as due to the presence of an ml 

 mentary layer. This has yet to be demonstrated by Hambach, who not only speaks 

 of it as an actual fact, but also makes use of it for classificatory purposes 3 . Thus 

 for example, he places in one division " all those species in which the horizontal 

 portion of the deltoid piece is very narrow, the sinus to both sides in the deltoid and 

 lancet pieces comparatively large, and so surrounded by the zigzag plated integument 

 that two of the so-formed openings appear externally only as one." 



The diagram which Hambach gives in illustration of this passage is supposed to 

 represent Pentremites sukatus ; but it is most remarkably different from the figure 

 of the natural summit of this species which he gave in his previous paper*. Five 

 spiracles are shown in the latter, situated very close to the peristome, from which they 

 are only separated by the narrow rim at the central ends of the deltoids, as shown in 

 our own figure (PI. I. fig. 10), and also in that given by Roemer 5 , who described the 

 species originally. In Hambach's later diagram, however, not only is there a separate 

 anal opening represented, but also ten spiracles, although, according to his description 

 of the type, there should be only five. The two openings of each interradius are 

 figured as separated by a portion of this elastic plated integument, a large area of which 

 also intervenes between them and the peristome, while there is a further extension 

 of it outwards between the spiracles and that portion of the deltoid which appears 

 on the exterior of the calyx. We find it difficult to understand the nature of the 

 preparation from which Hambach constructed his diagram, for his earlier figure of 

 the " summit of P. sukatus, not ground," correctly represents five spiracles close to 

 the peristome, and just separated from one another by the crenulated food-groo\e 

 while if the summit had been ground away sufficiently to show ten spiracles opening 



1 Ann. & Mag. Nat. Hist. 18S1, vol. viii. p. 121. 



2 Trans. St. Louis Acad. Sci. 18S4, vol. iv. part li. p. 539. 



3 Ibid. pp. 544, 545, fig. 5. * Ibid, part 1. L880, pi. a. fig. 1m. 

 8 Archiv f. Xiiturgesch. 1851, Jahrg. xvii. Band i. Taf. iii. fig. L0 6. 



I 'I 



