XI. Balanocrinus. 399 ~ 



Western Railway, the tunnel neai* Chalk Farm, Haverstock 

 Hill, Copenhagea Fields in Islington, Lambeth Hill in 

 Upper Thames Street, E.G., 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 from other localities occasionally retain the original 

 calcite, but this is usually impregnated 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 specimens ; but some fragments from Copen- 

 hagen Fields (E426) have been so little petrified that they 

 show the original structure of the stereom. 



The material includes th.e type-specimens of Penfacrinites 

 sowerbii (E 5888 a, h) and the original of Sowerby's figure 

 3 6 (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. On the other hand, these latter, in spite 

 of their general and occasional resemblance, display as a 

 group certain differences which justify their retention in 

 a separate species. 



The Normal Joint-face, in many specimens (e. g., E 426), 

 approaches nearer to the Isocrinus type than do any examples 

 of B. dldactylus, but in others it has the Balanocrinus cha- 

 racter ie. g., E 5887 a, b), and it is the latter that must be 

 compared with the normal B. didactylns. 



In a slightly quinquelobate internodalof 5*7 mm. diameter 

 (E 5887 6, Fig, 5) there are 7 or 8 peripheral crenellae to the 

 sector, at right angles to the peiiphery, evenly spaced so far 

 as one can see, straight, those near the iuterradius "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 *4 mm. long, in pairs gable-shaped and 

 alternating, but rapidly becoming shorter and opposed as 

 they near the centre. At I'l 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 clearlv 



