350 THE FOSSIL ECHINOIDEA 



it will be found that in zone a, the second plate immediately posterior to the peri- 

 stomial with two peripodia, is longer than broad, large, and has a peripodium at the 

 anterior and outer angle, close to the transverse suture between the first and second 

 plates. A few granules are borne upon it. Plate 3 is larger than the other two com- 

 bined, and is long and broader than the last. The peripodium is small and close to 

 the suture at the antero-external angle. The fourth plate is nearly as large as the third ; 

 but there is only a simple pore in it, and it is some distance from the anterior suture. 

 Plate 5 is about half the size of the last-mentioned, and is longer than broad ; the 

 pore is very small, and is nearer to the anterior and inner angle than to the outer. 

 The sixth plate is of course much smaller than the fifth, is broader than long, and is 

 placed obliquely, the greatest length being in the direction outwards and forwards. 

 This plate bounds the episternura externally, and towards the median line of the test is 

 only separated from its fellow plate -of the opposite side by the narrow junction of the 

 episternal and subanal plates. The plate is therefore one of those which are crossed 

 by the subanal fascicle, and the inner part is long from the median line outwards and 

 forwards. The pore is small, and placed close to the episternum at the inner and 

 anterior angle of the expanded part, which is external to the fasciole. The narrow 

 internal part of the plate forms with six other corresponding parts of plates one side of 

 the subanal plastron, which is limited by the subanal fasciole. The part of the plate 

 within the fasciole is broad from within outwards, and short in the antero-posterior 

 direction, and this is the shape of the other parts of plates entering into the con- 

 struction of the shield. 



The ornamentation of the plates within the fasciole is of a very elaborate kind, con- 

 sisting of a row of perfect small tubercles on each plate. The tubercles are minute near 

 the fasciole, and increase in size to the inner end of the plates. Plates 7 to 11 decrease 

 in size and breadth, for they are on the fiank of the widening interradial plate no. 4. 

 Each plate of this group has a part outside of the fasciole which is almost plain, and a 

 part within which has the ornamentation of the sixth plate. The pores are double in 

 each of these plates, and are placed on the anterior suture, just within the fasciole, and 

 in the narrow groove between the ornamented parts. The pores of each pair are close, 

 and are excavations in the sutural edge. The six pairs of pores form a curve within the 

 fasciole, and the last pair is remotest from the median line. Taking the other zone 

 into consideration it will be noticed that the peristomial plate (1, of b) has one peripodium 

 and a depression for a sphseridium, and that the plate is smaller than a 1. Plate b 2 has 

 one peripodial process and a sphseridium pit, and the posterior suture of this small plate 

 does not extend posteriorly to the anterior half of the plate a 2. Plate 3 is long and 

 narrow, and the imperfect peripodial process nearly occupies the whole of the anterior 

 part. Plates 4 and 5 are large, long, and broad, and the pores are small and near the 

 anterior sutures. Plate 6 is almost square, and is much larger than its fellow of zone 

 a; the pore is small and some distance from the anterior suture. Plates 7 to 11 

 are small and diminish in length and breadth ; they are more or less rectangular and 

 somewhat curved, with the convexity backwards. Their pores are single, and each is 



