348 THE FOSSIL ECHINOTDEA 



ever, the pair is only slightly diminished in size. The pairs of pores within the internal 

 fascicle are small, rather close, and quite as numerous as the others. The pores are 

 close, very small, except in the instance of the pair close to the fasciole, and their 

 direction is transverse near the small radial plate and a little oblique further out. 



The posterior poriferous zone within the fasciole has almost invariably, but not 

 universally, three or four pairs, of pores which are similar to those beyond the fasciole ; 

 they are smaller, especially that pair which is just within the fasciole and that nearest 

 the first very small pair. Usually the second of these larger pairs is nearly as large 

 as one of the outer set. The direction of these few pairs of pores is not in continuation 

 with the line of the posterior poriferous zone from the angle of the ambulacrum, for it 

 is almost transverse to the long axis of the test. 



The very small pairs which continue the larger set to the radial plate are seven or 

 eight in number, the pores are very small, and they are not separated by any ornament. 

 The little pairs, however, are in slight depressions which are sunken in a granular 

 ornament. The direction of their pores is forwards and a little outwards. 



The outer angle of the antero-lateral ambulacra is formed by the approach and 

 contact of the poriferous zones, not that the pairs of pores alter their direction and 

 close like the radii of a part of a circle. The interporiferous area diminishes in antero- 

 posterior dimension and becomes as it were thin, permitting the poriferous zones to 

 come in contact. This is owing to a diminution in the breadth of the ambulacral 

 plates towards the end of the series of great pores. Usually the poriferous plate at the 

 end of the posterior zones is smaller than the others, and it gives a preponderance in 

 length to those zones, for the pair on the outside of the anterior zones, corresponding 

 in position to that pair which has just been noticed, is very much smaller. This anterior 

 pair is in a simple depression, its pores are very small, and yet their direction is that of 

 the larger. Further out the antero-lateral ambulacra take a different direction from 

 those parts which have been described, become larger, both in height and in breadth, 

 and this expansion proceeds as far as the edge of the test, where narrowing and increase 

 in height occur. The direction of the lines of the pairs of pores of this part of the 

 ambulacra is not in continuation with that of the main poriferous zones, but is oblique, 

 and in the direction outwards and slightly forwards. On the side of the test the 

 ambulacra bend slightly, with a convexity forwards, and are in advance of the peristome 

 were a line to be drawn from it to the anterior edge of the ambulacral plates. 



The pores of these extra-petaloid plates are exceedingly minute, and their direction 

 is more or less transverse ; but after a few plates there is only one pore to each, and it 

 is not on the suture. 



"Below the edge of the test the plates diminish in breadth, and in a worn specimen 

 there are five seen, the last being in its proper zone at the peristomial margin. The 

 pores become larger on the actinal surface and are placed on the transverse sutures. 



At the peristome the plates are slightly broader than further out, but they are 

 not so high. In ambulacrum no. IV. the peristomial'plate of zone a has two peripodial 

 processes and that of zone h but one. Moreover the plate a is the larger. Oa the 



