BRACHIOPODA. 
9 
of the shell, and the substance of the valves is not pierced with 
minute perforations, though the sm-face 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 support a shelly band arising from the hinder 
or cardinal edge of the ventral valve. 
Fam. 1. Spiriferida. 
The oral arms very largely developed and supported the whole 
of their length by a thin shelly ? or cartilaginous ? spirally twisted 
plate. 
These shells are only known in the fossil state, hut the spiral 
supports of the arms are generally preserved, and may be dis- 
covered by sections of the fossil, and are often to be seen in the 
fractured specimens. 
This family is equivalent to the genus Spirifer of J. Sowerby 
the father, the family Delthyrida, M‘Coy, who gave some ex- 
cellent illustrations of the structure and the Spiriferidee of King. 
D’Orbigny proposed some genera under the names of Spiriferina, 
Spirigera and Spirigerina, according to the direction of the axis 
of the spiral cones, but it is douhtfid if these genera are only new 
names to those already established. 
The Spirifer of Sowerby, as reduced by M‘Coy, and the Mar- 
tinia of M‘Coy, have the hinge as long or longer than the width 
of the shell. In Atrypa, Dalman, and Athyris, M‘Coy, it is 
shorter and the shells oblong, rounder behind. 
According to the description of Mr. King, the genus Strigo- 
cephalus would appear to form the passage between this and the 
next family {Ann. Nat. Hist. xvui. 89). 
Fam. 2. RhynchonellideB . 
The oral arms are elongate, fleshy, supported at the base by 
two short, hard, diverging shelly laminae arising from the hinge- 
margin of the ventral valve. 
They are easily known from the Terebratulidm by the cavity of 
the shell being without shelly plates, its substance not perforated, 
and its surface being generally radiately plaited. 
Only one species, T. psittacea, is known in the recent state ; 
its animal has been described by Professor Owen. The family 
is equivalent to the plaited Terebratula of the elder James Sowerby 
and Von Buch, the non-perforated Terebratula of Carpenter, the 
genus Hypothyris of Phillips, and part of the family Terebratu- 
lidce of King. It contains the genus Rhynchonella of Fischer and 
D’Orbigny = Hypothyris of Phillips ; Camerophoria, King ; 
