GS 



sill C. WYTILLB TnOMSON ON THE MODE 01' 



The test of a full-sized example (fig. 6) is about 45 iniliims. in 

 length and 40 millims. in width ; the height of the shell in the 

 female is 25 millims., in the male it is considerably less. The 

 apex is nearly in the centre of the dorsal surface ; the genital 

 openings are three in number, in the female very large ; the bila- 

 Ijiate mouth is placed weU forward on the ventral aspect ; and the 

 excretory opening is posterior and supramarginal. The odd an- 

 terior ambulacrum is shallow and the tube-feet Avhich are projected 

 from it are large and capitate. The anterior paired ambulacra 

 are somewhat longer than the posterior. The whole of the surface 

 of the test is covered with a close pile of small spines of a dark 

 green colour; those fringing the ambulacral grooves are long and 

 slightly curved, and they bend and interdigitate so accurately 

 over the ambulacra that one might easily overlook the grooves at 

 a first glance. The peripetalous fascicle is somewhat irregular ; 

 but in those examples in which it is best defined, it forms a wide 

 arch extending backwards on each side a little beyond the lateral 

 ambulacra of the trivium, and then contracting a little, forms a 

 rudely rectangular figure round the bivium. The paved ambula- 



Fiff. 



Hemiaster, sp. Apical half of the test of a male example, from within. 

 Natural size. 



cral grooves in the male are shallow, not much deeper than the 

 anterior ambulacrum (fig. 7); in the female the pore-plates of 



