GYPIDIUM. MONOMY ARIA. rel 
remote, being separated by an ‘intermediate flattened area, 
varying considerably in breadth, in different species, and 
consists of three triangular parts, a central and two lateral 
ones ; this area is divided in the centre by a triangular pit 
for the passage of the byssus; within the smaller valve, and 
near the umbo, two spiral testaceous appendages are 
attached, whose convolutions diminish in size as they 
diverge from the centre of the shell. 
The central part seems to have been an aperture for the 
passage of a byssus, by means of which the animal probably 
attached itself to rocks and stones in the sea. 
Spirifer cuspidatus. Plate VII. fig. 8. Figs. 7, 9, and 
10 represent two spiral appendages. 
No recent species of the Spirifer are known, being only found in a fossil 
state. They are very numerous, and abound in the Mountain or Carboniferous 
Limestone, the Transition Limestone, and the Old Red Sandstone ; but none 
of them have been met with above the Magnesian Limestone ; most of the 
species are ribbed, grooved, or striated externally. 
Attention to the area between the beaks, and their internal spiral appen- 
dages, will at once distinguish the shells of Spirifer from the Terebratule, to 
which they are somewhat allied. 
This genus is properly divided into six sections, by Professor Phillips. 
Section 1. Cuspidate. Beaks imperforate, separated by a wide triangular 
area, the lower one not incurved ; upper valve convex ; hinge line generally 
straight, and equai to the breadth of the shell. 
Section 2. Augustate. Cardinal line as wide as the shell; valves with in- 
eurved beaks; mesial fold defined between two deeper furrows on the upper 
valve. 
Section 3. Radiate. Cardinal area not so wide as the shell; surface ra- 
diated. 
Section 4. Glabrate. Cardinal area not so wide as the shell; surface 
plain. 
Section 5. Terebrafuliformis. Devoid of a cardinal area, 
Section 6. Filose. Surface with prominent radiating threads. 
Genus VI.— GYPIDIUM. — Sowerby. 
Generic Character, — Shell inequilateral, inequivalve, 
the larger valve with an incurved umbo, remote from the 
hinge; one valve divided by a central septum into two 
parts; the other by two septa into three unequal parts ; 
umbones imperforate and incurved, 
Gypidium Aylesford. Plate VIL. fig. 19. Found in the 
Dudley Limestone, and is a characteristic member of the 
Silurian rocks. 
This genus was established by Sowerby under the name of Pentamerus, but 
as that name is preoccupied by a genus of insects, we have adopted the name 
of Dalman ; who also denies that the shells ofthis genus are quinquelocular, 
