SEA-tTECHINS AND SEA-CUCUMBEE8. 329 



in being slender tliroughont, and in having the knobbed 

 calcareous stalk extending np to the head, which ap- 

 pears to work on it. In each of the other sorts the 

 stalk extends only through a part of the distance, above 

 which the investing fleshy neck becomes wider and 

 empty. 



But the internal structure is not quite the same as 

 in the others. The main portion of the head is com- 

 posed of gelatinous flesh ; the calcareous support being 

 reduced to that ridge which runs up the interior side 

 of the blade. This is somewhat bottle-shaped, with a 

 bulbous base, and a long slender neck, with two edges 

 on the inner face, which are armed with horizontal 

 hooked spines, some of which are double, and the whole 

 terminates in a sort of ring, formed by the last pair of 

 spines, which unite into the acute horizontal point that 

 I have already mentioned. The skeleton is filled with 

 oval cavities like that of the others. 



The fourth kind of Pedicellaria, which I call P- 

 stereopTiylla, is quite distinct from either of the others. 

 It is very minute, the head being only 2 } o^h of an inch 

 in height. The head is a prolate solid spheroid, cut 

 into three segments, exactly as if an orange were di- 

 vided by three perpendicular incisions meeting at the 

 centre. Thus the blades meet accurately in every part 

 when closed, but expand to a horizontal condition. 

 These are almost entirely calcareous, being invested 

 but thinly with the gelatinous flesh. They are filled 

 with the usual oval cavities, set in sub-parallel arched 

 series. 



The head is set on a hollow gelatinous neck nearly 

 as wide as itself, and thrown into numerous annular 

 wrinkles ; its walls are comparatively thin, disclosing a 



