CONTENTS. 
Sponr/. 3 
Page 
(iii) Mesozoic.23 
(a) General ....... 23 
(b) Cretaceous ...... 23 
(c) Jurassic ....... 23 
(d) Lias.23 
(e) Trias........ 23 
(iv) Pakeozoic.23 
(a) General ....... 23 
(b) Permian ....... 23 
(c) Permo-Carboniferous .... 23 
(d) Coal-Measures ...... 23 
(e) Lower Carboniferous . . . . 23 
(f) Devonian ....... 24 
(g) Silurian ....... 24 
(h) Ordovician ...... 24 
(k) Cambrian ....... 24 
(l) Pre-Cambrian ...... 24 
IV. Systematic. 
a. Porifera, general ........ 24 
b. Calcarea .......... 24 
(i) Homoccela ........ 24 
(ii) Heteroccela ........ 25 
c. Hexactinellida . . . . . . . . . 27 
(i) Lyssacina ........ 27 
(ii) Dictyonina ........ 28 
d. Demospongise ......... 31 
(i) Tetraxonida . . . . . . . . 31 
(a) Carnosa . . . . . . . 31 
(b) Tetractinellida . . . . . . 31 
(1) Choristida . . . . . 31 
(2) Lithistida ..... 32 
(ii) Monaxonida ........ 35 
(a) Hadromerina.35 
(1) Aciculina ..... 35 
(2) Clavulina ..... 35 
(b) Halichondrina .... .36 
(c) Incertse Sedis . . . . . . 41 
(iii) Iveratosa ........ 41 
(a) Dictyoceratina . . . . . . 41 
(b) Dendroceratina ...... 43 
(iv) Myxospongida ....... 43 
E. Octactinellida ......... 43 
F. Heteractinellida ........ 43 
g. Incertae Sedis ......... 43 
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