THE BUMMIT-PLATES. 67 



plates, which on close examination, however, prove to be Bryozoa or ovulum-like 



bodies." He supported this statement in a later paper 1 by asserting that " Shu- 

 mard's original specimen of Pentremites Sayi, which was figured bj 1'. I!. Meek, 



and is now in the collection of the Washington University, proves to hav< ly a 



covering of minute calc-spar crystals on the summit, leavings of the Burrounding 

 matrix, which could easily be removed by applying a moist camel's-hair brush to 

 them." 



Although, of course, we have not seen Shumard's specimen, yet, thanks to Mr. 

 Wachsmuth, we have been able to examine many examples both of Schizoblastus 

 (Pentremites) Sayi (PI. HI. figs. 2,3) and of Granatocrirms Worwoodi (PL VII. 

 figs. 3, 4, 10-13). They both occur in the Upper Burlington Limestone, and we 

 have not the smallest doubt that the closure of the central summit-opening is a 

 perfectly natural condition in both species. But this causes us to have considerable 

 doubt whether, after all, Shumard's description (with Meek's illustrative figure) of 

 the summit-plates in Scliizoblastus Sayi is not more accurate than llambach's 

 assertion that the plates in question are merely calc-spar crystals, " leavings of the 

 surrounding matrix ;" and we venture to think that it would be perfectly safe to 

 permit Hambach to attempt their removal by applying a moist camel's-hair brush 

 to them. Did the specimen belong to us, we should not hesitate to offer it to him 

 for experiment. 



Three years after the publication of the Missouri Report, Shumard 2 met with a 

 specimen of Pentremites conoideus, which "was found to exhibit very clearly the 

 structure represented in pi. ix. fig. 4. The central stelliform space (mouth) is 

 perfectly closed by six small microscopic plates, a central one of a pentagonal form, 

 surrounded by five smaller pentagonal pieces, which unite with the edges of the 

 aperture and form a little dome." Shumard's figure certainly bears out his descrip- 

 tion. But according to Hambach 3 , his original specimen " does not show anything 

 of the remarkable structure represented in the figure;" and its appearance is simply 

 due to the oolitic character of the rock in which it was imbedded. We cannot but 

 think, however, that a skilled palaeontologist like Dr. Shumard would scarcely have 

 mistaken what Hambach calls "ovulum-like bodies" for more or less regular cal- 

 careous plates, such as had been previously described by Roemer in Ekeacrinus 

 Verneuili. 



It would be very interesting to know what view Hambach takes of the summit- 

 plates of the latter type which are represented in PI. XVIII. fig. 10. He admits 4 

 that " the condition of life was undoubtedly a similar one " throughout the whole 

 class of the Blastoidea; and as he totally denies the existence of summit-plates in 

 Pentremites, he is bound to give some explanation of those described by Roemer in 



1 Trans. St. Louis Acad. Sci. 1884, vol. iv. no. 3, p. 540. 2 Ibid. 1853, vol. i. no. 2, p. 243. 



3 Ibid. 1884, vol. iv. no. 3, p. 541. ' Ibid, p. 517. 



