\in. (Ujathocruius. 219 



III I5r from .'{ to 7. 'I'lie lower Muinbtn-.s are more usual, 

 and the higher numbers, when tliey occur, arc in the branches 

 on the inner side of the dichotoin ; thus, the left posterior 

 arm of E 1450 (PI. XIII. tig". 2) has III Br, counting from 

 left to right, — 3 . 4 . . 6 . 4 *. Here, too, the second ossicle 

 is sometimes liiglicr than the first. 



IV Br from 3 to 9. In this case the lower numbers are in 

 the branches on the outside of the arm, the higher numbers 

 on the inside of the dichotoms, and the middle numbers on 

 the inside of the arm. This arrangement will be better 

 understood from an actual example: in 57362 B. M. the quarti- 

 brachs run thus, from left to right — 4 . 8 . . 9 . 7-6 . 6 . . 7 . 5. 



V Br from 3 to 11. Generally speaking these numbers 

 follow the same sort of arrangement as in previous series, but 

 the higher numbers are often finials, especially in rather 

 young si)ecimens. Thus in an arm of 57480 B. M. (PI. XIII. 

 tig. 1), starting from the middle or inner side of the arm and 

 passing towards the outer side on the right, the numbers run 

 as follows, / being placed against the finials — 6 .9.-8/. 6/- 

 6 . 9/'. . 9/"'. 8. 



VI Br from 2 to 14. Many of these are generally finials, 

 and in young specimens even the lower numbers are finials. 

 Otherwise the arrangement is much as in the quintibrachs. 



VII Br are only found in well-grown specimens. The 

 numbers observed are 3 and 4. They are always finials ; but 

 it is of course conceivable that the arms migiit branch yet 

 once more in an exceptionally well-favoured individual. If, 

 however, finials appear in any one series, it seems to be the 

 rule that all of the ensuing series shall be finials ; that is to 

 say, in no single arm does one branch ever get more tiian one 

 series ahead of the other. 



The above numbers do not take account of 206 Holcroft, 

 in which the series are rather longer, 17 being seen in one 

 internode. 



Anal structures. — The measurements of anal x in E 1450 

 are as follows : — Height 4*5 millim. ; width below, 38 

 millim. ; width above, 4*75 millim.; that is to say its width 

 is about g that of the adjacent radials (PI. XIII. rig. 2). It 

 supports a large proximal median plate and a smaller plate 

 on either side [rt and It). The latter plates rest partly on the 

 adjacent radials. 



The Ventral Sac is about half the length of the arms or 



* In this aud in the ensuing examples tlie peculiar spacing of the 

 niunbers is an attempt to represent the bilateral symmetry of the arm : 

 the two l)ruuche.s of each dichotom are separated by only a single lull- 

 stop. 



