CONTENTS. Spong. 3 
Page 
(iii) Mesozoic . . ..19 
(a) General (vacant). 
(b) Cretaceous.19 
(c) Jurassic . . . . . . . 19 
(d) Lias (vacant). 
(e) Trias (vacant). 
(iv) Palaeozoic.19 
(a) General (vacant). 
(b) Permian.19 
(c) Permo-Carboniferous (vacant). 
(d) Coal-Measures (vacant). 
(e) Lower Carboniferous . . . . 19 
(f) Devonian (vacant). 
(g) Silurian.19 
(h) Ordovician.19 
(k) Cambrian (vacant). 
(l) Pre-Cambrian (vacant). 
IV. Systematic. 
a. Porifera, general . . . . . . . . 20 
b. Calcarea (including Astroscleridce) ..... 20 
(i) Homoccela .......; 20 
(ii) Heterocoela.20 
c. Hexactinellida . . . . . . . . . 21 
(i) Lyssacina ........ 22 
(ii) Dictyonina ........ 23 
d. Demospongiae ......... 26 
(i) Tetraxonida ........ 26 
(a) Carnosa ....... 26 
(b) Tetractinellida ...... 27 
(1) Choristida.27 
(2) Lithistida ..... 28 
(ii) Monaxonida ........ 30 
(a) Hadromerina ...... 30 
(1) Aciculina ..... 30 
(2) Clavulina ..... 30 
(b) Halichondrina . . „ . . . . 31 
(c) Incertae Sedis.37 
(iii) Keratosa ........ 37 
(a) Dictyoceratina ...... 37 
(b) Dendroceratina (vacant). 
(iv) Myxospongida (vacant). 
e. Octactinellida (vacant). 
f. Heteractinellida (vacant). 
G. Incertae Sedis . 
38 
