XI. Balanocrinus. 399 
Western Railway, the tunnel near Chalk Farm, Haverstock 
Hill, Copenhagen Fields in Islington, Lambeth Hill in 
Upper Thames Street, E.C., and Hornsey. 
The specimens from Sheppey are all pyritized, and many 
of those from the older collections have decomposed. Those 
from the Hampstead neighbourhood are mostly in limonite. 
Those fro other localities occasionally retain the original 
calcite, but this is usually impreguated with iron or changed 
into one of the above forms. The state and mode of preser- 
vation usually obscure the joint-faces and often alter the 
shape of the specimeus; but some fragments from Copen- 
hagen Fields (E 426) have been so little petrified that they 
show the original structure of the stereom. 
The material includes the type-specimens of Pentacrinites 
sowerbii (H 5888 a, 56) and the original of Sowerby’s figure 
36 (57539 ; see under “ Conclusions,” p. 405). 
The resemblance of these specimens to those of B. didac- 
tylus from Biarritz is so great that foreign authors, relying 
mainly on figures, have more than once suggested that such 
or such a variation in the latter was conspecific with one or 
other of the British forms. It has here been shown that 
the Biarritz specimens, in spite of their differences, are 
linked by gradations into a single species. One form alone, 
therefore, cannot be taken out for association with one of 
the British forms. Ou the other hand, these latter, in spite 
of their general and occasional resemblance, display as a 
group certain differences which justify their retention im 
a separate species. 
The Normal Joint-face, in many specimens (e. g., E 426), 
approaches nearer to the Jsocrinus type than do any examples 
of B. didactylus, but in others it has the Balanocrinus cha- 
racter (e. g., E5887 a, 6), and it is the latter that must be 
compared with the normal B. didactylus. 
In a slightly quinquelobate internodal of 5:7 mm. diameter 
(E 5887 0, Fig. 5) there are 7 or 8 periphgral crenellae to the 
sector, at right angles to the periphery, evenly spaced so far 
as one can see, straight, those near the interradius -4 mm. 
long, those near the radius ‘7 mm., externally confluent. 
Radial ridge-groups begin with 3 or sometimes 4 pairs of 
crenellae, at first 4mm. long, in pairs gable-shaped and 
alternating, but rapidly becoming shorter and opposed as 
they near the centre. At 1l*l1 mm. from the periphery, 
along the radius, these give place to the parallel adradial 
ridges, which pass into a raised central area. The ridge-pair 
has a width of ‘9 mm. and the radial canal is not clearly 
