610 SCHIZASTER CANALIFERUS. 



towards the actinal and abactinal side. The edge increases in height in the 

 same proportion with the increase in the height of the test. The posterior 

 interambulacruin forms a rounded keel. In the middle of the plates of the 

 posterior lateral interambulacra, near the upper part of the edge, there are two 

 or three nodes, forming a disconnected keel, extending to the actinal surface. 



The actinal surface is convex ; the whole posterior extremity is rounded; 

 the actinal side and the high posterior edge of the test running into each 

 other, so as to form a continuous surface ; the ambitus is only indifferently 

 defined, in the anterior portion of the test. The anal system is placed in 

 the upper part of the posterior extremity, which is slightly depressed, and 

 slopes towards the posterior hh]^ of the actinal plastron, forming a shallow 

 depression between the two rounded nodes, which connect the actinal plas- 

 tron with the posterior extremity of the test. 



This species is remarkable for the great breadth and depth of the odd 

 anterior ambulacrum. It forms a rectangular groove, attaining its greatest 

 breadth a short distance from the apical system. The sides of the groove are 

 vertical, slightly convex outwardly ; the broadest part of the groove is about 

 in the middle; where the peripetalous fasciole crosses this groove it is slightly 

 narrower, shallower, becomes rounded, and is gradually lost at the actino- 

 stome ; the pores are irregularly crowded, closely packed at the base of the 

 angle of the vertical sides of the groove. The median I interambulacral) 

 line forms a keel between the odd groove and the lateral anterior ambulacra, 

 extending to the peripetalous fasciole, and continued as independent nodes 

 to the edge of the actinal surface ; a narrow, indistinct keel is formed nearer 

 the groove which commences at the fasciole, consisting of two or three con- 

 nected nodes. 



The posterior lateral ambulacra are very short, petaloid, rounded at the 

 extremity, with broad poriferous zones. The anterior lateral ambulacra are 

 elongate, more sunken than the posterior, slightly broadest near the extrem- 

 ity, which flares outward ; the pores are of the same size, elliptical, pointed, 

 connected by a shallow groove. The abactinal extremity of the lateral 

 ambulacra is narrow, pointed, with narrow poriferous zones; in the posterior 

 ambulacra this rudimentary part is in the trend of the petals; in the anterior 

 ones it forms nearly a right angle with the general trend of the ambulacra. 

 The peripetalous fasciole crosses the posterior interamhulacrum, pointing to- 

 wards the posterior edge; it runs from the extremity of the posterior ambu- 

 lacra, nearly parallel to the general trend of the anterior lateral ambulacra, 



