12 CATALOGUE OF THE BLASTOIDEA. 



of Blastoids. The basals are quite small in Granatocrinus (PL VIII. figs. 13, 18; 

 PL IX. figs. 3, 4, 9, 13), Mesoblastus (PL VI. figs. 9, 14 ; PL VIII. figs. 3, 8), Acen- 

 trotremites (PL XIII. fig. 17), and Schizoblastus (PL VI. fig. 17). But they form a 

 more orless elongated cup in Pentremites pyriformis and its allies (PL II. figs. 24-30), 

 Troostocrinus (PL V. figs. 21, 22; PL XII. fig. 11), Pentremitidea (PL IV. figs. 9,11, 

 13, 16, 18), Phcenoschisma (PL XI. figs. 5, G ; PL XII. fig. 10), Codaster (PL XII. 

 figs. 2, 3, 5, 6 ; PL XIII. figs. 10, 12, 15), and Orophocrinus (PL XV. figs. 1, 3, 6, 9). 

 They probably reach their maximum length relatively to that of the calyx in Crypto- 

 schisma Schulzi (PL V. figs. 25, 26). On the other hand, the deltoids of this genus 

 are scarcely visible externally. In the original of PL XIII. fig. 20 they are confined 

 to the summit ; but in the specimen represented in PI. V. fig. 24 one of them is just 

 visible at the top of an interradius. As this figure shows, however, they take a large 

 share in the formation of the radial sinus, and the same is the case in Codaster and 

 P/uinosc/tisma, in neither of which genera are they properly visible at the sides of the 

 calyx (PL X figs. 18-20 ; PL XL figs. 1, 2, 3, 5, 6 ; PI. XII. figs. 1-6, 10 ; PI. XIII. 

 figs. 3, 9-12 ; PL XIV. figs. 1-5, 8-12). The same is the case in Troostocrinus and 

 Pentremitidea, which have still more reduced deltoids, owing to the constriction of 

 radial sinuses (PL V. figs. 1-11, 15-21). But they seem to be relatively large and 

 visible externally in Hall's Pentremites ?eda, which we are inclined to refer to Pen- 

 tremitidea on account of its other characters (PL V. figs. 12, 13). 



On the other hand the deltoids are relatively very large in Schizoblastus Sayi and 

 in S. Rofei (PL III. figs. 1-3 ; PL VIII. fig. 9), and in Granatocrinus Derbiensis 

 (PL IX. figs. 1, 2, 6), the radials being very greatly reduced and only enclosing quite 

 small portions of the tips of the ambulacra (PL IX. figs. 3, 4). This condition 

 reaches its maximum in El&acrinus, which has quite small basals, so that the whole 

 of the calyx, with the exception of the very limited dorsal surface, is formed by the 

 interradials (PL II. figs. 45 & 46). This genus is further distinguished by the 

 presence of an anal plate which divides the posterior deltoid into two parts 

 (PL XVIII. fig. 19). 



C. The Basals. 



The genus Pentremites was described by Say ' as having a pelvis of three unequal 

 pieces, two being pentagonal and one quadrate (PL V. fig. 29). Goldfuss 2 , however, 

 was led to believe that Pentremites had five basals like most Crinoids ; but this error 

 was pointed out by Rocmer 3 , who confirmed Say's description and illustrated it by a 

 good figure. This tripartite division of the base of the Blastoids has never been 

 further disputed ; but it is a different division from that which presents itself in 



1 Journ. Acad. Nat. Sci. Philad. 1825, vol. iv. pt. 2, p. 292. 



2 Petrefacta Gennaniaj, Th. i. 1826, p. 100. 



3 Archiv f. Naturgesch., 1851, Jahrg. xvii. Bd. i. pp. 326-329. 



