346 THE FOSSIL ECHINOIDEA 



of the median line. The madreporite may be traced in some specimens in between the 

 basals " 2 " and " 3 " ; again, a similar intrusion of it exists between the anterior and 

 posterior basals, a few foramina being seen as lateral offshoots of the main mass of the 

 madreporite. The apex of this triangle is close to the posterior suture of the second 

 plate. The pairs of pores for the ducts of the generative glands, and the pores 

 themselves are close: the anterior pair are slightly smaller than the posterior, and are 

 closer, rather oval in outline, and their long axis is oblique, the direction being outwards 

 and forwards and therefore away from the long axis of the test. The anterior pair of 

 basals are small and the openings occupy the greater part of them. The lateral basals 

 behind these last are larger, and their pores are larger than those just mentioned, and 

 although but slightly varying from a circle in outline, it is clear that their long axis is 

 directed forwards and slightly inwards. 



The anterior ambulacrum is very long, and is very narrow on the dorsum. The 

 divergence of the poriferous zones is very slight from the apex to the margin ; there 

 it contracts again for a short space and again expands before reaching the peristome. 



At the commencement and near the radial plate, the pairs of pores are numerous 

 and close in succession, and the pores, placed one before the other, are separated by a 

 small but prominent granule. Further out, but still within the line which would unite 

 the transverse portions of the antero-lateral ambulacra, the pairs of the pores of the 

 anterior ambulacrum are in slight depressions surrounded with a minute granulation. 

 As the plates are large near the position of the crossing over of the internal fasciole, 

 the pairs of pores are further apart there, and their distance increases gradually to the 

 margin. On the actinal surface the plates of the ambulacrum are large, and expand so 

 that the second from the peristome, on both of the ambulacral zones, is the largest. 



The peripodial processes of this, and indeed of all the ambulacra, are large, ear- 

 shaped, slightly sunken below the level of the granular surface of the test, slightly 

 tumid around, or on one side of the pore, which is usually elongate. The peristomial 

 margin of the ambulacrum has the plate on zone " b " large, and of course perforated 

 by two pores, each in a peripodial process ; but the edge of that plate corresponding to 

 the interradium no. 3 is not straight, but has a re-entering angle placed on a line with 

 the space between the two peripodial processes. Hence the plate is nipped in as it 

 were, and this condition existing in the plate " a " of ambulacra no. 4 increases the 

 breadth of the peristomial plate of the interradium 3. The peristomial ambulacral 

 plate " a " has the usual soUtary pore, and is decidedly smaller than its neighbour of 

 the zone "J," The plate is contracted near the margin, and the second plate of the 

 same zone comes not very far from the peristome, so that its peripodial process lies 

 anterior, and towards the median line in relation to the pore of the marginal plate. 

 The peripodial i)rocess of this marginal plate is nearer the margin of the peristome than 

 that of the plate of zone " b," and this last is nearer the median line of the ambulacrum 

 than the other. The expansion of the actinal plates of the ambulacrum is almost without 

 ornament ; but the plates are very sparely marked with distant, yet distinct, granules ; 

 the sutures are in shallow depressions, and the plates are slightly tumid. There are 



