298 I. IJIMA : HEXACTINELLIDA. I. 



Contents. 



Page. 



Introduction 1 



Topography of the Sagami Sea. (PI. XIV) 6 



Collecting Hexactinellida and other deep-sea animals in the Sagami Sea 16 



Methods used in the studies 32 



EUPLECTELLID-ffi:. 



Eupledella Owen 37 



Key to the species of Eupledella 58 



Euplectella imperialis Ij. (Pis. I & II) 59 



General characters 60 



Spiculation 69 



Young specimens 79 



Miscellaneous notes. (Affinity of the species. Regeneration. Commensal immates) ... 83 



Euplectella marshalli Ij. (Pis. Ill, IV & V) 86 



General characters 88 



Spiculation 96 



Young specimens 103 



Soft Parts 116 



General arrangement of the soft parts and their relation tu the spicules ... 117 



The dagellated chamber 128 



The trabeculœ 147 



Cells in connection with trabecular 165 



* Archseocytes 165 



Thesocytes 173 



lieproductive elements 179 



Suminaries of the histology of E. viarshidll 190 



Development of hexasters 192 



Miscellaneous notes. (Affinity. Regeneration. Commensal inmates) 200 



Euplectella oweni Herkl. & Marsh. (PI. VI) .. 202 



General cluuacters 204 



Spiculation 211 



Miscellaneous notes. (Abnormal sieve-plate. Commensal inmate, &c.) 215 



Euplectella curvistellata n. sp 217 



A\'.7af/;-e//a O. ScHM 220 



Regadrella okiiioseana IJ. (Pis. VII & VIII) 223 



General characters 224 



Spiculation 229 



Young specimens 239 



Soft parts 247 



Miscellaneous Notes, (llelation toi2. decora. Malformations.) 248 



Regadrella komeyamai Ij- (Pis. IX à X) 252 



General cliaractcrs 252 



Spiculation 258 



