710 



ME. T. T. GEOOM ON" SOME 



(a) The commonest variety is represented in PL XXVIII. fig. 1. 

 The largest seen (fig. Id) measured about 1 millim. in length. In shape 

 they are conical and each consists of three valves which fit neatly 

 and tightly together. I could detect no teeth on them. They vary 

 in size ; each valve is broadest at its base, and is furnished with a 

 rounded knob close to the point of attachment. In front it narrows, 



Pig. 5. — Oral Surface of Pelanechinus corallinus (restored). 



Nat. size. 



and then expands again to a broad spoon-shaped piece. The in- 

 terior of the valve is shown in figs. 4 e and /*. The lower 

 portion is seen to be divided by a median crest, which in recent 

 pedicellarise gives attachment to the muscles connecting the valves 

 togethert . This variety only occurs in a depression immediately 

 surrounding the imbricating plates. They probably have long stems. 



* Fig. 1/is very diagrammatic. 



t P. Greddes, Trans. Eoyal Soc. Edinburgh, vol. xxx. part i. p. 383. 



