450 



MOLLUSCA. 



pedicle-notch beneath the beak of the ventral valve, and 

 Eichwaldia (also Silurian) has the peduncle transmitted 

 through a foramen in the ventral umbo. Porambonites, 

 again, of the Lower Silurian possibly the type of a distinct 

 family though its shell-structure is really impunctate and 

 fibrous, is readily recognised by the fact that the surface is 

 ornamented with minute close -set circular 

 pits. Lastly, the genus Camarophoria (fig. 

 296) may be regarded as a link between 

 RhyncJionella and Pentamerus, since it pos- 

 sesses the general form of the first, together 

 with the converging dental plates of the latter. 

 The genus is found in the Carboniferous and 

 Permian deposits. 



All the preceding forms are naturally as- 

 sociated with one another by their structural 

 characters ; but there is another great group of 

 Brachiopods usually placed in the Rliyncliond- 

 lidce, and agreeing with this family in many points, of which 

 the genus Pentamerus is the type, and which presents certain 

 distinctive features of its own. In Pentamerus (fig. 297) the 

 shell is ovate, the valves articulated by teeth and sockets, the 



Fig. 296. 

 arophoria globulina. 

 Permian. (After 

 King.) 



Fig. 297. Penlamerus Knlglitii. The right-hand figure shows the internal septa and 

 dental plates of the shell. Upper Silurian. 



surface generally ribbed or striated, but sometimes smooth. 

 The beaks are incurved, that of the ventral valve concealing 

 a triangular fissure. Inside the ventral valve " two contigu- 

 ous vertical septa coalesce into one median plate, extend- 

 ing from the beak to a greater or less distance; and then 

 diverge and form the dental plates, enclosing a triangular 



