ADVERTISEMENT TO SECOND FASCICULUS. vil 
was proved by microscopic and other characters, to be the silicious axis of a Gorgonian 
zoophyte, allied to the recent Hyalonema of the Chinese seas. (See p. 10). 
On the corals, generally, great labour has been bestowed; the characters of most of them 
being now first noted in detail, and their internal structures ascertained by vertical and hori- 
zontal sections. Many new genera and species have been made known and figured; and 
species, supposed to be common to the Cambrian, Silurian, and Devonian rocks, have been 
discriminated by tangible characters. 
Those curious fossils from the Devonian slates of Polperro, supposed by all previous 
observers to be scales, teeth, bones, and fin-rays of fishes, partly Devonian and partly Upper 
Silurian species, have been proved, from examination of the Cambridge specimens, to belong to 
the Amorphozoa, or Sponge-group, forming a new genus (Steganodictyum), fragments of which 
are figured on Pl. 2. A. 
To avoid the confusion and error arising from the constant misapplication of the undefined 
terms ‘pelvis, ‘costals,’ ‘scapule,’ &c., proposed by Miller, and used by most subsequent 
authors with various meanings to designate the plates of Crinoids, a new and simple system of 
nomenclature has been proposed (p. 52), applicable alike to the most complex or most 
simple forms. 
At page 124 a new Order is established for the Echinites of the Paleozoic rocks, and it is 
pointed out that they will not accord with M. Agassiz’ view of the quinquepartite composition 
of the crust of the sea-urchins, applicable, without exception, to all those of the newer rocks 
and recent seas. 
At page 139 the homologies of the Cephalic shield and eye-line of Trilobites have been 
investigated for the first time, with reference to the variations made known by anatomists in 
the rings forming parts of the head and mouth, in the whole group of recent Crustacea of 
higher organisation. Attention is also drawn to an indication of antenna, the supposed want 
of which in those creatures has hitherto obscured their affinities. 
All the great groups have been taken in zoological order, and each is introduced by such 
condensed remarks, as the space allowed of, on the zoological and anatomical characters of the 
living analogues, as will enable the academic student using this Catalogue in the Museum, to 
form just notions of the place in the organic scale of the various fossil types, and dispel certain 
false popular notions of “progressive development.”—At the foot of page 191 is a notice of a 
discovery, first made by Professor M*Coy some years ago, from some recent specimens in the 
Museum, (recently published by Mr Woodward since those sheets were printed off,) that the 
valves of Terebratula are opened by the action of a pair of muscles—a contrivance without 
parallel in Conchology. Naturalists formerly supposed that Terebratula, having no cartilage 
like Lamellibranch bivalves, to force the valves open, opened them by inflating the arms, or 
by the pressure of the elastic loop; neither of which explanations could be structurally cor- 
rect. The present explanation obviously applies to all Brachiopods. 
In matters of nomenclature, priority in specific names has been carefully observed; and 
the exact relation of synonyms to each other is rendered more obvious and exact than in 
