404 



DR F. A. BATHER. 



entirely in the foot-half, and occupies a tract close to the sole and parallel with the 

 upwardly curving frame (PI. III. figs. 27, 31, 33, 34). Here are a number of roughly 

 elliptical areas, each with its long axis at right angles to the frame. The number 

 varies slightly within the species, possibly increasing with the age of the individual. 

 In such a large individual as G45, the number is fifteen, and probably this is almost the 

 maximum for the species. The ratio of the two diameters of the ellipse is 1 : 3. The 

 actual measurements vary slightly with the size of the individual, and the ellipses 

 towards the ends of the tract are smaller than those in its middle region. In G45 the 

 long diameter of the full-sized ellipses is 3 mm., and the length of the whole tract 

 is 177 mm. 



§ 196. Each elliptical area is in this species surrounded by a raised rim, which 

 clearly marks it off from the adjoining integument (text-fig. 16). This rim is divided., at 



Fig. 17. Fig. 18. 



Fig. 16. 

 Text-figs. 16-18. — Cothurnocysiis Elizac, elements of the subvective system, enlarged about 12 diameters. 



Fig. 16. — External view of two grooves. That on the left is drawn directly from G45 ; it sliows the shape of 

 the short u and the long U, and the slight rebate for cover-plates on the latter. That on the right shows 

 a similar groove, with the cover-plates in position, on the evidence of G17 and other specimens. 



Fig. 17. — Internal view of a groove, based mainly on G 36, in which the elements are relatively long and 

 distinct from those adjacent (cf. PI. III. fig. 35). 



Fig. 18. — Internal view of a groove, drawn from G 10, in which the elements are relatively short, and appear 

 as though joined to those adjacent (cf. PI. III. fig. 36). 



about two-thirds the distance from its outer end, into an inner short u and an outer 

 long U, meeting by their free ends, towards which the substance of the rim tapers. 

 The outer edges of the rim are rounded, but the inner sides are steep, being almost 

 vertical in the short u, but having in the long U a slope plainly visible to anyone 

 looking from above, and lying so as to make the inner boundary of the long U more 

 V-shaped than U-shaped. 



§ 197. These essentials of the structure are confirmed by those specimens which 

 yield an imprint of the interior {e.g. G36). There project into the thecal cavity bold 

 V-shaped ridges, with the free ends of the V slightly enlarged so as to butt on the free 

 ends of the short u-shaped ridges (text-figs. 17, 18). These enlarged ends probably 

 served as fulcral planes over which the free ends of the short u could glide. Thus in 

 several specimens, seen from the outside, the short u seems to be pushed up so as to 



