64 CATALOGUE OP THE BLASTOIDEA. 



and in the same paper he describes how the integument of microscopic plates which 

 covers the peristome of Granatocrinus Norwoodi passes out between the tube-like 

 spiracles "in a double series of plates, and was evidently continued far down the 

 central grooves of the ambulacral fields." These observations were confirmed by 

 Meek and Worthen x in 1869, and extended to Cryptoblasttis melo and Schizoblastus 

 Sayi. In all four species they found " the central opening covered by small pieces, 

 and continuing out from these, a double series of minute alternating pieces a short 



distance along the mesial furrows of each pseudo-ambulacral area These little 



pieces do not fill the linear furrows, however, but cover them over, so as to leave a 

 small canal passing along under them, and under the little vault covering the central 

 opening, in such a manner as to communicate through the latter with the visceral 

 cavity within the body." 



The first figure, showing these covering plates of the ambulacra, was that of 

 Orophocrinus stelliformis, which was given by Meek and Worthen 2 . They are seen 

 extending outwards from the peristome over the narrow proximal ends of the 

 ambulacra, which lie between the deltoids, just as in our PI. XV. figs. 11, 12 ; 

 though to judge from the American figure the arrangement of the plates seems to 

 be somewhat more regularly alternating than in our specimen. 



Wachsmuth and Springer 3 have also given a figure illustrating the same point in 

 Schizoblastus Sayi. But Hambach 4 declares that his specimens " which show a 

 similar covering as in this last-named figure, prove that the covering consists only of 

 fragments of broken-up pinnulge which were washed into the ambulacral furrows and 

 remained there." We will not venture to dispute that this may be the case in 

 Hambach's specimens ; but we should like to know the nature of the proof which 

 satisfied him that the plates forming the covering of the ambulacra really do consist 

 of fragments of broken-up pinnules ; and even if this be the case (which we doubt) 

 it is no argument against the existence of covering plates in other specimens which 

 he has not seen. On PI. III. fig. 3 we give a similar figure to that published by 

 Wachsmuth and Springer of the summit-plates, and their extension over the proximal 

 ends of the ambulacra in Schizoblastus Sayi; while the same thing is shown in 

 Orophocrinus stelliformis in PI. XV. fig. 12, and also in one ambulacrum of Grana- 

 tocrinus Norwoodi in PI. VII. fig. 13. We have seen other specimens of all three 

 species which illustrate the same point ; and we fully agree with White, Meek and 

 Worthen, and with Wachsmuth and Springer that the covering is a natural one, and 

 by no means of such an accidental character as Hambach makes out. 



The regular alternating arrangement of the ambulacral covering plates is most 



1 Proc. Acad. Nat. Sci. Philad. 1869, pp. 84, 85. 



2 Report Gcol. Survey Illinois, 1873, vol. v. pi. ix. fig. 5. 



3 Revision of the Palseocrinoidea, Part II. 1881, pi. xix. fig. '6. 



4 Trans. St. Louis Acad. Sci. 1884, vol. iv. no. 3, p. 540. 



