390 Dr. F. A. Bather on British Fossil Crinoids : 



crinus generally, tlie radial excavation is never great, 

 althou^^h often exaggerated by the crushing to -svhich these 

 stems seem ])eculiarly liable. Thus in a rather small and 

 slightly crushed pentapetalon (E 22028) IR is 2'7 mm., and 

 r. 1*9 mm. But in a well-marked pentapetalon of 7"3 mm. 

 diameter (E 219G1) the measurements are IB 3*6 mm., 

 r. 2*8 mm. 



Since IR here equals half the diameter, the depth of the 

 radial excavation is '8 mm., or less than one-ninth of the 

 whole. The outline of the joint-face, however, is in some 

 specimens more petaloid than the cross-section at the 

 middle of the columnal, because the radial pore lies at the 

 bottom of a depression, which, as viewed from the joint-face, 

 produces the illusory efl'ect of a radial triangle. Thus the 

 number of peripheral creuellae is increased to 14 or more; 

 the length of the radial ridge-groups is correspondingly 

 lessened, but they are still com])osed in part of adradial 

 crenellae following on the periplieral crenellae, so that on 

 the w hole the peculiarly Balanocrinid effect is obscured. At 

 the same time the petal-floors are necessarily narrower, and, 

 owing to the change in the radial ridge- groups, cease to be 

 bounded by concave curves ; they assume, therefore, a sub- 

 lanceolate or kite-shaped or pyriform outline similar to that 

 of the normal Isocrinus petal. In such forms the crenellae 

 near the interradius usually cease to be confluent, so that in 

 this region the suture is crenelate. Yet even in these forms 

 the fused portions of the radial ridge- groups manifest their 

 Balanocrinid nature. 



The Syzygial Faces, both epizygal and hypozygal, depart 

 from the normal in the greater development of the crenellae. 

 In a specimen with mean diameter 9'4 mm. (E 22027 ; 

 Fig. 2) the main peripheral crenellae of a sector are still 

 about 14, but, instead of being confluent, they tend to 

 increase in number towards the periphery, either by forking 

 or by intercalation of narrower shorter crenellae, or in both 

 ways. An intercalated crenella on the epizygal corresponds 

 to a fork on the opposed hypozygal, and vice versa. In the 

 specimen referred to, which is a rounded pentagon with 

 slight tendency to lobation, the normal crenellae on the 

 interradii are still short, about 0"6 mm. ; but the crenellae 

 become gradually longer as the radius is ap|)roached, so that 

 some attain a length of 16 mm. The inner ends of these 

 long crenellae die away gradually into the floor, and in some 

 cases two normal crenellae may join, so that from a single 

 stem spring tw^o main branches, each of which forks again, 



