XI. Balanocrinus. 403 



about I'O mm., the middle one (Order III) in each case 

 being very slightly higher than the two others (Order IV). 

 The difference iu diameter can scarcely be measured, aud 

 probably does not amount to more than "05 mm. on the 

 outer angles, but it is more apparent on the re-entrant 

 sides. 



Forbes said that the section was more stellate in younger 

 specimens. There is, however, no correlation at all between 

 size and stellatiou or lobation, but the correlation with 

 alternation that does exist indicates that the proximal region 

 is more stellate or lobate. 



This leads us to consider the two specimens hitherto 

 separated as Pentacrinus sowerbii (E 5888, a, b). They 

 Avere fairly well I'cpresented in Sowerby's engravings (fig. 4) ; 

 a is the fragment in matrix, b the isolated fragment. They 

 belong, however, to a single stem, which has broken at the 

 syzygy so that the epizygal with 2 facets is on b and the 

 hypozygal on a. The cirrals attached to the epizygal are 

 shown at the top end of Sowerby's figure. Diameter 

 5'4 mm. ; section quinquelobate. In b are 25 iaternodals, 

 which appear to be in three orders, though possibly it should 

 be four. The height of the epizygal (Order I) is 1*3; that 

 of Order II about I'O; of Order III -9 to -8 ; of Order IV 

 *6 to '5 mm. The arrangement, starting at the proximal 

 end is iii, iv, II, iv, iii, iv, II, in, iv, II, iv, in, II, 

 HI, IV, II, III, IV, II, IV, III, II, IV, III, I. The differences 

 between the orders are more marked in their diameters, 

 and may amount to *5 mm., but the condition of the 

 specimen renders exact measurement difficult. 



Owing to the confluence of the crenellae iu most cases, 

 the suture-line is rarely crenelate. The following speci- 

 mens, however, show some crenelation at the interradial 

 angles : 57542 a, d, e, E 21967, E 21969. All these are 

 somewhat lobate or stellate. Crenelation might be detected 

 in other examples were it not for their patination. Its 

 presence, of course, indicates that the crenellae have not yet 

 become confluent so as to form an entire margin — for 

 instance, the association of a crenelate suture-line with 

 confluent crenellae, as in Forbes's fig. 10, is merely evidence 

 of inaccuracy. Crenelation is therefore rather a sign of 

 youth, or, in conjunction with lobation, of recent formation 

 as in the proximal region. As one would expect therefore, 

 crenelation is best seen in P. sowerbii, where it is almost 

 obscured on fragment i, but very clear on fragment a. In 

 the latter the crenelation extends over the sutural margin 

 down the side-face towards the equator of the columnals 



27* 



