240 Messrs. K. Etlieridge, Jun., and P. H. Carpenter oil 



tions "*. In this we entirely concur. G. Noriooodi possesses 

 very large radial plates, extending- from the edge of the 

 hollow base almost to the very apex of the calyx, and corre- 

 spondingly small orals. On the other hand, in the British 

 species, although the radials maintain their general superiority 

 of size in all but one species, the orals are larger than in the 

 American type. A gradation, however, is traceable in G. 

 j)isifbrmtSy in which they are smallest, to G. orbiculan'Sj 

 which possesses the largest oral plates with the exception of 

 G. derbiensis. In the latter they attain an inordinately large 

 size, the radial plates being only just sufhciently high to en- 

 close within their sinuses the distal ends of the long ambu- 

 lacra. The spiracles o])en in all the species, whether the oral 

 plates are large or small, on the mamillary projections at the 

 apices of the latter t ; but in G. jn'styonnis they are bounded 

 externally by nodular elevations of the plates. Dr. C. A. 

 White has shown that the anal Sjiiracle in G. Noriooodi is 

 bordered on the outer side by a solid ])rojection formed by a 

 part of the oral plate \. Meek and Worthen suggested tlurt 

 the anal plate consisted of three pieces § 5 but we have not 

 met with any evidence contirming this view. 



The ambulacra of Granatocrinus are always long, curved, 

 and narrow, and reaching to the base — the calyx usually 

 resting, when placed on its base, on the distal ends of the 

 ambulacra. This appears to be an essential character of the 

 genus, and is one of the points in which it agrees with Schizo- 

 hlastus. The side plates in the ambulacrum of Granatocrinus, 

 unlike those of Peutremites, do not lie against the sides or 

 edge.s of the lancet-plate, but actually upon it, so as to conceal 

 the greater part of it. The portion left exposed is the crenu- 

 lated ridge of the lancet-plate, bearing the zigzag ambulacral 

 or food-groove. This is the structure in G. ellipticus, G. 

 cam^yaimlatitSj G. orhicidaris, and G. derbiensis, whilst in 

 G. Noricoodi it is perhaps more exposed than in any other 

 species we have as yet been able to refer to this genus. The 

 side plates are variable in number according to species (from 

 twenty to eighty), and are usually transversely elongated. 

 The ambulacra are at times deeply impressed within the 

 prominent edges of the radial forks. 



A good deal of variation is shown in the formation of tJie 

 pores. In G. orbicularis they are enclosed between the mai-gin 



* Illinois Geol. Report, ii. p. 275. 



t First pointed out in G. Norwoodi by Owen and SLuuiard (Joiirn. 

 Acad. Nat. Sciences Philadelphia, 1850, ii. pt. 1, p. 64). 

 X Boston Journ. Nat. Hist. 180-3, \ii. no. 4, p. 483. 

 § Illinois Geol. Surv. liep. 187J3, p. 465. 



