Tin: SUMMIT-PLATES. 75 



The summit of Granatocriwas Norwoodi seems to vary m a similar manner. The 

 individuals figured in PL VII. figs. 4, 13, show traces of proximals arranged around 



an ore-central ; whereas in other cases no great regularity is visible in the grouping of 

 the summit-plates (PI. VII. rig. 11). 



It sometimes happens that impressions of the summit-plates appear in internal 

 casts, as shown in that represented in PI. VI. fig. 20, in which the impressions of 

 the orocentral and of the four anterior proximals are tolerably distinct. A somewhat 

 less regular arrangement appears in the case of Sckizoblastus Sayi, which we figure 

 on PI. VI. fig. IS ; and Shumard * described the summit-plates of his specimens as 

 being arranged in a manner somewhat similar to those of Roeraer's Elceacrinus 

 Verneuili', but in other specimens of this type it is difficult to distinguish the 

 orocentral and proximals among the number of other plates in the summit. \\< 

 have no question, however, that these are perfectly natural in character, and not, as 

 Hambach 2 asserts, either fragments of matrix, Bryozoa, or any other foreign bodies. 



1 Palaeontology, Swallow's 1 Bt and 2nd Annual Report Oeol. Survey Missouri, 1855, pt. 2, p. 186. 



2 Trans. St. Louis Acad. Sci. 1880, vol. iv. no. 1, p. 150. 



