1 80 CLYPEASTERI.E. 



is this : the ambulacra! plates are much broader than the 

 inter-ambulacral, consequently the two ambulacra nearest 

 to each other appear to belong to the same pair, whereas 

 each belongs to a different pair. That such is the case is 

 proved by the position of the oviducal pores, which are 

 seen at the heads of the narrow or inter-ambulacral spaces. 

 There are four of these pores instead of five, the one want- 

 ing being the anal pore. At the heads of the ambulacra! 

 spaces there are also minute pores, which are probably in 

 the living animals filled up with ocular points, as in the 

 Echinus. The ambulacra are curved, and diverge greatly 

 towards their extremities ; each is furnished with about 

 forty pairs of pores for the exsertion of suckers. These 

 pores are somewhat distant from each other, and connected 

 by a deep furrow. Down each ambulacral space runs a 

 smooth groove, which is continued round the under surface 

 to the mouth. The inter-ambulacral plates are minutely 

 but irregularly rugose, with spiniferous granules. The 

 ambulacral are also granulated, but in a more complicated 

 manner. That portion of their surface nearest the inter- 

 ambulacral spaces is granulated irregularly, but the rest 

 is occupied by granules of two sizes arranged in alternate 

 rows, which slope towards the ambulacral grooves. A 

 similar arrangement is seen on the under side, with the 

 addition that the grooves have a border of minute tuber- 

 cles or granules, analogous to the border avenue-spines of 

 the Starfish. The vent is lenticular, and is placed quite 

 on the upper margin in a notch ; there is a short groove 

 beneath it, which is connected with a smooth shallow 

 furrow leading to the mouth. The base is almost flat ; if 

 anything, slightly concave. The mouth is placed in the 

 centre ; a pentangular space resembling an Asterina, on 

 which the tubercles are irregularly placed, surrounds it, and 



