RHYNCHONELLID. Bulli 
valve is so much developed as to give the whole shell the external 
appearance of an Orthis. 
CAMERELLA, Billings, 1859. 
Syn.—Triplesia, Hall, 1859. 
Distr.—9 sp. Lower Silurian; North America. C. Volborthi, 
Billings. 
Ventral valve with a small triangular chamber beneath the 
beak, supported by a short mesial septum as in Pentamerus. 
Dorsal valve with a single mesial septum and two short lamelle 
for the support of the oral appendages, as in Rhynchonella. 
Surface smooth or obscurely plicated. 
EicHwa.piA, billings, 1858. 
Etym.—Dedicated to Professor Eichwald, the celebrated 
Russian paleontologist. 
Distr.—3 sp. Silurian; Canada, England. JZ. subtrigonalis, 
Billings. 
Shell with the ventral valve perforated on the umbo for the 
jassage of a peduncle; the place of the foramen beneath the 
beak being occupied by an imperforate concave plate; the 
interior of each valve divided by a medio-longitudinal ridge, 
that of the dorsal valve very prominent; hinge and teeth sockets 
wanting. 
The internal structure of the ventral valve somewhat resem- 
bles that of Pentamerus or Camarophoria. 
CAMAROPHORIA, King, 1844. 
Distr.—Fossil, 9 sp. Carb.—Permian (Magnesian limestone) ; 
Germany and England, N. America. C. Schlotheimi, Busch 
(exxxvi, 82). C. crumena, Martin (cxxxvi, 83, 84). 
Ventral valve with converging dental plates supported ona 
low septal ridge; dorsal valve with a prominent septum sup- 
porting a spoon-shaped central process; oral lamellz long and 
slender. Foramen angular, cardinal process distinct. 
PENTAMERUS, Sowerby, 1813. 
Etym.— Pentameres, five-partite. 
Distr.—Fossil, 52 sp. Upper Silurian—Devonian; Arctic 
America, United States, Europe. P. Knightii, Sby. (exxxvi, 
85-87). 
Shell impunctate, ovate, ventricose, with a large incurved 
beak; valves usually plaited; foramen angular; no area or del- 
tidium ; dental plates converging, trough-like, supported on a 
prominent septum; dorsal valve with two contiguous longitudinal 
sept opposed to the plates of the other valve. 
Oral lamelle have been detected by Mr. Salter in P. liratus ; 
