282 Dr. P. H. Carpenter on the 



summit-plates are an integral part of tlie organization of a 

 Blastoid. 



Not content with impugning the accuracy of Shumard's 

 figure of Pentremites conoideus, Mr. Harnbach now asserts 

 that " Shumard's original specimen of Pentremites Sayi*, 

 which was figured by F. B. Meek and is now in the collection 

 of the Washington University, proves to have only a covering 

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

 surrounding matrix, which could easily be removed by 

 applying a moist camel's-hair brush to them." Not having 

 seen Shumard's specimen, I can offer no opinion as to the 

 respective merits of the descriptions of it which have been 

 given by him and by Mr. Harnbach. But I have carefully 

 examined several examples of this species with the summit 

 closed, and the covering of the central opening does not con- 

 sist in any case either of " leavings from the surrounding- 

 matrix," " ovulum-like bodies," or Bryozoa. Granatocrinus 

 Norwoodi and Orophocrinus stell iformis occur in the same 

 formation (the Burlington Limestone j"), and in both of them 

 a group of summit-plates has been described and figured by 

 Messrs. Meek and AVorthen \. I have seen it in both these 

 species, and have not the smallest doubt that the structure in 

 question is a natural covering and not a merely accidental one. 

 I do not dispute that there may be Bryozoa, ovulum-like 

 bodies, or any other accidental coverings on the specimens 

 which Mr. Harnbach has seen ; but it is scarcely logical for 

 him on the strength of these observations to make the some- 

 what sweeping assertion that the central opening was never 

 closed by additional plates. Theory counts for nothing in 

 such a case ; while the observations of Romer and of the best 

 American palaeontologists are directly at variance with 

 Hambach's dictum. 



Mr. Harnbach § also tells us that his reason for not men- 

 tioning the covering of the ambulacral furrows of the Blas- 

 toids Avas " that I always found them in such a form or con- 

 dition as to make on me the impression that they were mere 

 accidental coverings, nor did I see any good reason for their 

 presence ; " and he goes on to say that his specimens " prove 



* Geol. Surv. Missouri, 1855, pi. B. fig-. 1 c. 



t G. Norwoodi and Schizoblaxtus (Pentremites)] Sayi occur in the 

 upper division and O. stelliformis in the lower division of this lime- 

 stone. 



\ ' Palaeontology of Illinois,' vol. v. p. 466, pi. ix. figs. 2 a, 5 ; and 

 Proc. Phil. Acad. 18G9, pp. 84, 85. 



§ Trans. St. Louis Acad. vol. iv. p. 540. 



