XI. Balanocrinus. 401 



The series of pits bordering the floors explain the incised 

 lines sotnetimes seen in this position on the weathered fossils, 

 e. g., 57542 d. The looser stereom of the flooi's being more 

 readily weathered, these tracts are often deeper in the fossils 

 than they can have been in life. Sometimes advanced 

 Aveathering or decomposition emphasizes this greatly (57551 o) 

 and also brings ont the weak structnre of the stereom under 

 the radial canal ; in decomposing pyritized specimens tlie 

 colnmnals break into pentameres along the radial planes, 

 though in crushed specimens {e. g., 57542 a) the cracks 

 usually follow the lines of interradial weakness. Thus is 

 brought out here, as in B. didactyJus, the difference between 

 the original pentamerism and the secondary concentration of 

 tlie stroma fibres along interradial pillars. 



Between the Isocrinus and Balanocrinus types of normal 

 joint-face there seems to be every possible gradation. There 

 are no grounds for supposing that the material comprises 

 two species, and consequently it cannot comprise two 

 genera. 



The Syzygial Joint-face of an Epizygal is well shown in 

 57543 c {cf. W. H. Bajly's drawing in Forbes, pi. iv. fig. 8, 

 which, for all its inexactness, gives the general appearance 

 well). There are 2 facets; diameter parallel to a line 

 joining the facets 5*5 mm. ; diameter at right angles to this 

 5*0 mm. Corresponding with the facets the radial tracts 

 are raised, as in B. didadylus, though not quite so markedly. 

 Peripheral crenellae about 7, broadening outwards and 

 confluent ; length on the interradius "2 mm., gradually 

 increasing to 1*0 mm., but these long ones die away into the 

 floor. Radial ridge-groups comprise about 3 pairs of 

 reduced obscure crenellae, rapidly decreasing in size towards 

 the centre, and tending to lie at right angles to the radial 

 canal ; this last is little more than a fine line, and is bordered 

 by no raised ridges. Petal-floors flush. 



'Che Hypozygal joint-faces are not clear; apparently they 

 correspond, mutatis mutandis, to the epizygal face, but are 

 not so strongly marked. One of the clearest is in 57513 b. 



The Transverse Section of the stem is generally sub- 

 cylindrical, usually varying towards either pentagonal or 

 cjuinquelobate, as in all figures of Sowerby and Forbes. 

 The specimens seen by J. S. Miller were no doubt sub- 

 pentagonal — hence the name subbasaltiformis. Those in 

 J. Woodward's collection were probably subcylindrical, like 

 other Entrocho-Asteriae. Quinquelobation may occasionally 

 be marked, but no specimen can be called stellate, though 

 that condition is approached by 57541 and E 21926. 



Ann, & Mag. N. Hist. Ser. 8. Vol. xx. 27 



