LOI'TCSIA FROM ItRITlSU COLUMIIIA. 75 



tiibly bo compared with that given on plute Ixxix. fig. 1 of Messrs. 

 Carpenter and IJrady's rnoinoir, a indicates a part of the primary 

 hiruina, which is thickened, as before described, and may consequently 

 be seen as a series of ratlier broad dark zones, indefinite oti tlieir inner 

 edges, and runniii!,' parallel to each olher. i points out one of the 

 beeondiiry gnnvtlis or sejtta; these maybe seen running parallel to the 

 longiludinal axis of the form. They ai)pear wi(U', from being cut ob- 

 licinely, but also, in many cases, from the identilii^alion with them of the 

 htngitiidinal rods or rafters formed by the ex])ansi()n of the pillars. 

 At right angles to these, at /, are seen rods formed by the nni(m, trans- 

 verse, to the axis, of the distal ends of the pillars. At c the section 

 becomes nearly radial, and the pillars are seen as in figure 2. At d 

 part uf the thiekened primary laiiiiiui is shown in plan. (X-o.) 



Fig. 4 is nearly longitudinal and radial, representing part of three folds of the 

 jn-iniary lamina (ri) and the pillars uniting them (c). The irrcmla- 

 rities of tiii'se are shown, and the cancellated growth from the inner 

 side of the lamina is indicated by //. (x T.'i.) 



Fig, 0. Portion of tlu^ thickened primary lamina shown in plan. At c/ the 

 greater part of the spimgy thickening has been removed in grinding 

 down the section. The rafter-like thickenings from the intersections 

 of which the colunnis 8i)ring are here clearly .seen. The darker zone 

 sun- )iMuiiiig this part represents tiie primary lamina and its thicken- 

 ing (//) ohli(|ucly cut. Where, at the edges, the section becomes more 

 nearly at right angles to the curved lamina, the piUars may be seen 

 running out. (x 75.) 



Fig. 0. Transverse section through the nucleus of a very young specimen, show- 

 ing the first convolutions. (X 4.'>.) 



Fig. 7 represents the external form of the organism of actual size. The figure 

 on the right is of au unusually long variety. 



