490 PROF. P. M. DUNCAN ON THE GENUS DIRRHOPALUM. 



great attenuato-acuates, and the shafts radiate at nearly right 

 angles. The oviform bases are in contact at their sides with their 

 fellows, and at their ends with the great spine, which they sur- 

 round (PI. XXIX. fig. 30). The axial canal is not to be seen. 



The body-spicula in contact with the spine of the Echinus 

 are short, curved, cylindrical, having globose or subhemispherical 

 ends, slightly constricted where they join the body of the spicule. 

 They are entirely bluntly spined. The spinulation is small and 

 close on the rounded ends ; but there is less of it on the constricted 

 necks, and it is wider apart, stouter, and longer on the body. 

 The boss-shaped ends are wider than the body (PL XXIX. fig. 19). 

 Usually a large axial canal is visible in these spicula, and it 

 extends far into the heads of the elongated curved dumb-bells. 

 These spicula form one or two layers, one above the other ; they 

 are placed close together, without order as regards their direc- 

 tion ; but there is some diversity in their size and shape, owing 

 mainly to age. 



A typical spiculum of this kind has a perfectly cylindrical body? 

 not more swollen out in any part than elsewhere ; the cylinder, 

 slightly bent, is narrower than the terminal bosses, and is more 

 than double the length of one of them. 



The blunt spinulation surrounding the whole surface is irre- 

 gular, distant, and the tops of the projections, whieh differ in 

 length, are blunt. 



Varieties. — Spicula of the same length as the type, but having 

 the boss more spherical and the constriction of the neck more 

 decided, the spinules being scanty on the neck and larger than 

 usual on the body. Spicula with one boss perfect and the other 

 less so or smaller. 



In all, the spinulation of the boss-like ends is minute and in 

 a series of concentric circles ; but there is no order in that of the 

 curved stems, where it is larger. 



The diameter of these body-spicula is -j-^ inch, and the length 

 ^inch. 



The sarcode covered the radiating whorled spicula and the 

 spaces between them ; it closed in the spaces or interstices 

 between the numerous whorls, and it extended further out, to 

 the tops of the long skeletal spicula. The spicula of the derm 

 are few in number ; and some are apparently quite superficial. 

 Three kinds are to be noticed ; but one appears to be a young 

 form. One is a minute cylindrical rod ; another is of the same 



