74 Mr. H. J. Carter on the close Relationship of 



EXPLANATION OF PLATE VIIL 



N.B. Figs. 1-6, 10, 12, 21, and 23 are on the scale of l-48th to l-1800tli 

 inch, fig. 9 on the scale of l-96th to l-1800th, and fig. 14 on the 

 scale of l-96th to l-2700th inch ; all the rest are of the natm-al size. It 

 should he remembered that the ground-work of figs. 8, 11, 15, 16, 18, 

 and 19 is granulated, but too small to be represented in a drawing of the 

 natural sizej hence the white groimd must be considered as such; the 

 granulation being produced by the weathering out of the interstitial 

 matter of the tortuous anastomosing tissue-fibre of which the organisms 

 respectively were composed. In figs. 20, 22, and 24, this granulation, of 

 course, is not present, as they are taken imm fresh sections, 



Fig.l. Hydractinia eclmiata. Vertical section of skeleton, magnified; 

 composed of chitinous tissue-fibre, a, primary lamina ; b, pri- 

 mary interval ; c, secondary lamina ; d, secondary interval ; e e, 

 small spines, free and connected with the secondary lamina re- 

 spectively ; /, sm-face of third lamina and that of the Hydrac- 

 tinia ; g, large spine. 



Fig. 2. The same. Horizontal section of base of large spine : a, closed 

 summit of same. 



Fig. 3. The same. Fragment of ccenosarcal stolon-like tubulation creep- 

 ing over the sm-face, forming corresponding grooves in the latter 

 and connected with the interior, a, annulation; 6, the same, 

 truncated to show the diaphragmatic form of the constrictions ; 

 c, points of chitine (^'horn cells ") on the part sinking into the 

 interior. 



Fig. 4. Hydractinia calcarea, n. sp. Vertical section of skeleton, magnified ; 

 composition calcareous, a, primary lamina; b, primary in- 

 terval ; c, secondary or surface-lamina ; d, small spines, free, and 

 connected respectively with secondary lamina ; e, spines on secon- 

 dary or surface lamina ; f, large spine ; gg, chitinous diaphragms 

 leading from the apertures on the sm-face (fig. 5, c e c) to the 

 primary interval. 



Fig. 5. The same. Diagram of portion of surface to show : — a a a, large 

 spines ; bbb, ai-ea of small spines, not delineated for perspicuity ; 

 ccc, apertures leading down through short tubes respectively 

 into primary interval ; d d d, interstitial fossae, smooth, not 

 spined ; e e, hole of the diaphagm as seen through the apertm-e. 



Fig. 6. The same. Horizontal section of base of large spine, a, form of 

 columnar cavity ; b, closed summit of large spine. 



Fig. 7. Hydractinia plioce^ia, AUman, (fossil), natural size ; vertical 

 section, a a, Buccimim ; b b, Hydractinia, showing the " inter- 

 vals " in the form of chambers, arranged in horizontal lines, cut 

 vertically by radiating tubes. 



Fig. 8. The same. Portion of natural sm-face, natural size, showing : — 

 a, large spines ; b b, grooves formed by ccenosarcal tubulation 

 (fig. 3) ; c, circular area, to which the apertures of the surface 

 are added, aU the rest having been omitted for perspicuity. 



Fig. 9. The same. Vertical section of fragment of surface of last-formed 

 ''lamina and intervals," magnified, showing how the vertical 

 tubes on each side of the interval or chamber, being opposite, 

 might appear in the general section to be continuous, a, small 

 spines of natural surface ; b, apertures in natural surface ; c, 

 anuulated tubes leading down from apertures to intervals ; ddd, 

 chambers or intervals ; e, spines remaining free in intervals. 



