PALJ£ONTOLOG V. 



93 



to the apertural gap, joined by similar parallel furrows extending 

 into the apex ; on the other side the furrows abut against it at an 

 acute angle, and decrease in length as they ascend. The central 

 gap is not indicated on the outside, because the furrows on both 

 its sides are parallel with it, as new plications are never intercalated 

 in this place. 



The annexed sketches will cause the descriptions to be under- 

 stood at a glance. We perceive, by looking at the figures, that 



APERTURAL GAP. 



CENTRAL GAP. 



LATERAL GAP. 



in the apertural gap the striae must have a pinnate position, 

 because on both of its sides new plications are constantly added 

 to the ends of the fascicles ; for the same reason we see them on 

 the lateral gap on one side pinnate and on the other parallel, 

 because no new plications are ever inserted there, and in the cen- 

 tral they are all parallel because no implantation occurs on any of 

 its sides. 



All Zoantharia rugosa have this structure, but the four principal 

 septal divisions do not present themselves in all with equal con- 

 spicuousness. In some the cycle of plications in the calyces is 

 almost uninterrupted, and they appear as if of truly radial structure j 

 in others the division lines between the fascicles are well marked 

 by gaps, which on the bottom of the end-cells dilate into depres- 

 sions called septal fovcce. The apertural fovea is always the largest, 

 and an indication of it is noticeable in all forms of this order, while 

 the two lateral gaps rarely become so distinct as to dilate into 

 septal foveae. The central'gap is almost in every instance obscure, 

 scarcely noticeable. Mr. Kunth, in speaking of the position and the 



