74 Mr. II. J. Cai-ter on the close RelationsMp of 



EXPL.VNATION OF PLATE VIII. 



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

 inch, tig. on the scale of l-OOth to l-1800th, and lig. 14 on the 

 scale of"l-tHJth to l-2700th inch ; all the rest ai-e of the uatiual size. It 

 should be rruumibored that the gi-ound-work of %s. 8, 11, 15, IG, 18, 

 and 11) is gi-auulatod, but too small to bo represented in a drawing of the 

 natural size; hence the white grovuid must be considered as such; the 

 graiuilation being produced by the weathering out of the interstitial 

 matter of the tortuous anastouiosiug tissue-libre of which the organisms 

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

 coiu*se, is liot present, as they are taken horn, fresh sections. 



Fi(j. 1. Hydradinia echinata. Vertical section of skeleton, magnified j 

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

 maiy 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 Ilydrac- 

 tinia ; y, large spine. 



Fiy. 2. The same. Horizontal section of base of large spine : «, closed 

 summit of same. 



Fiy. 3. The same. Fragment of ccenosarcal stolon-like tabulation creep- 

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

 and connected with the interior, a, auuulation ; b, the same, 

 truncated to show the diaphragmatic form of the constrictions ; 

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

 interior. 



Fiy. 4. Hydradinia calcarea, n. sp. Vertical section of skeleton, magnified ; 

 composition calcai-eous. a, primary lamina; b, primary in- 

 terval ; c, secondary or smface-lamiua ; (/, small spines, free, and 

 connected respectively with secoudai-y lamina ; e, spines on secon- 

 daiy or sm-face lamina ; /. large spine ; yy, chitinous diaphragms 

 leading from the apertiu-es on the sm-face (fig. 5, c c c) to the 

 primaiy interval. 



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

 spines ; bbb, area 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 

 spiued ; e e, hole of the diaphagm as seen through the aperture. 



Fiy. 6. The same. Horizontal section of base of large spine. «, fomi of 

 columnar cavity ; b, closed summit of large spme. 



Fiy. 7. Hydradinia pliocena, AUman, (fossil), natural size ; vertical 

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

 vals " in the foi-m of chambers, arranged in horizontal lines, cut 

 vertically by radiatiui^- tubes. 



Fiy. 8. The same. Portion ot natural sm-face, natural size, showing : — 

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

 (fig. 3) ; c, circular area, to which the apertm-es of the surface 

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



Fiq. 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. «, small 

 spines of natural surface ; b, apertm-es in natural surface ; c, 

 annulated tubes leading dowTi from apertm-es to intervals ; ddd, 

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



