402 DR F. A. BATHER. 



§ 181. Marginal 5 is a simple short piece. 



v^ 182. Marginal 6 is longer and curved, forms the ball of the foot, and bears a knob, 

 recognised in G6, Gl2, G26, G40, G42, G55, G56, G58 (PI. III. figs. 26, 36). 



§ 183. Marginal 7 continues the upward curve towards the toe, and it also bears a 

 knob (G26, PI. III. fig. 26). 



§ 184. Marginal 8, the toe-piece, is prolonged into an upturned point or fixed spine, 

 which appears as a rule to have curved inwards, i.e. towards the leg of the boot, as in 

 G26 (PI. III. fig. 26), although in G45 (PL III. fig. 31) it seems to be curved outwards. 

 It is rarely visible, probably because it rarely lay precisely in the extension-plane of 

 the theca ; but whether it was defiected as a rule away from or towards the reverse face 

 [i.e. hypothetically towards the sea-floor) is not clear from the evidence. At its proxi- 

 mal end this piece is forked, one quite short branch resting on marginal 7, the other 

 branch, which is longer, passing on to the top of the foot and meeting — 



§ 185. Marginal 9, a three-rayed piece, of which a long horizontal branch meets the 

 process of marginal 8 just mentioned, while of the two other branches one passes up to 

 the leg, the other down to meet the upward process of marginal 4, with which it com- 

 bines to form the strut (PL III. fig. 26). It should be remembered that the latter pro- 

 cesses are only on the reverse face of the theca, so that the strut does not divide the 

 thecal cavity, a fact which is obvious in PL III. fig. 31. 



§ 186. Marginal 10 continues the upward process of marginal 9, and forms the 

 front of the leg. At its upper end it widens and abuts on a broad flattened marginal 

 11, only seen completely on the reverse face (PL III. fig. 30). These two pieces (10 

 and 11) support the tongue process (§ 190). 



§ 187. The flattened piece 11 meets a similarly flattened piece 12, springing from 

 marginal 1, and the two bridge over the opening of the leg on the reverse face only 

 (PL III. figs. 28, 30). Marginal 12 sends a narrow flattened process down the whole 

 inner side of marginal 1 (G 22). These two marginals support the tag process 

 (§ 189). 



§ 188. The knobs mentioned in the preceding account of the marginalia are con- 

 fined, if not entirely, at least with very rare exceptions, to the reverse face of the theca. 

 They project from the marginals, usually at right angles to the plane of extension, so 

 that it is very difl&cult to trace their course or to appreciate their length in the fossils. 

 In some specimens they appear to be short stout processes, for which the term " knob" 

 is perfectly appropriate, but in others they appear to have been produced into rather 

 long spines not very unlike the toe-spine. These diff'erences probably depended on 

 the immediate environment of each individual (§ 234). The knobs have been observed 

 on the reverse face of marginals 2, 3, 3a, 4, 6, and 7. Their normal and most constant 

 positions seem to be at the heel (marginal 3), at the ball of the foot (marginal 6), and 

 half-way between these points and the top of the leg (marginal 2) and the toe 

 (marginal 7) respectively. But, even when others are developed, as on 3a and 4, all 

 are confined to the lower or proximal half of the theca. 



