46 
Class II. BRACHIOPODA. 
Subclass I. ANCYLOPODA. 
The oral arms not extensile, or only at the tip, on fixed shelly 
supports, or in grooves in the under or ventral valve. The mantle 
is adherent to the shell, the substance of the shell being pierced 
with numerous minute perforations, which are pervaded by the pro- 
cesses of the mantle. 
Order I. Ancylobrachia. 
The oral arms are attached to two shelly plates arising from the 
hinder or cardinal edges of the ventral valves ; they are recurved 
and convolute on the inner side of the lamina. The animal is 
generally attached to marine bodies by a tendinous peduncle, which 
passes through an aperture in the apex of the umbo of the larger 
or dorsal valve. The peduncle and the aperture are sometimes 
obliterated in old specimens. 
Fam. 1. Terebratulidce. 
1. Terebratula. 
1. T. , t. 380. f. 4. 
2. T. Sowerbyi, t. 380. f. 5-9. 
3. T. , t. 381. f. 1. 
4. T. caput serpentis, t. 381. f. 6. 
5. T. truncata, t. 381. f. 4. 
Order II. Cryptobrachia. 
Oral arms entirely attached, in the form of two or more lobed pro- 
cesses sunk into the grooves in the disk of the ventral valve. Shells 
thick, generally attached by the outer surface of the larger valve. 
Fam. 1. Thecideada. 
1. Argiope. 
2. Thecidea. 
Subclass II. HELICTOPODA. 
The oral arms elongate, regularly spirally twisted when in repose. 
The mantle lobes merely applied to the inner surface of the shell. 
The substance of the valves is not pierced with minute perforations, 
though the surface is sometimes spinulose, the spines being only 
formed on the edge of the shell while it is being increased in size. 
Order III. Sclerobrachia. 
The oral arms supported by a shelly band arising from the hinder 
or cardinal edge of the ventral valve. 
