BRACHIOPODA. 



Family III. — Ehyxchonellid^..* 

 Eatojn^ia, Hall, 1859. 



Dedicated to tlie late Professor Amos Eaton. 



Examples, Atrypa peculiaris, Conrad ; A. singularis, Yaniixem. 



Bliell like that of Rliynchonella ; the xower half of the ventral 

 valve with a broad deep sinus. Yalves articulating by means 

 of two teeth in the ventral valve, with corresponding sockets in 

 the dorsal valve, and a median septum embraced between the 

 deeply bifurcating cardinal process of the opposite one. 



Dorsal valve with four crural processes ; in the ventral valve 

 the dental plates are represented by elevated lamellae surround- 

 ing the muscular impression, which is much stronger and differs 

 in some respects from that of Pihynclionella. 



Fossil, 7 species. Upper Silurian. United States. 



Camerella, Billings, 1859. 



Examples, C. Yolborthi, Billings ; Atrypa extans. Hall. 



Synonym, Triplesia, Hall, 1859. 



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 lamelloo 

 for the support of the oral appendages, as in Rhynchonella. 

 Surface smooth or obscurely plicated. 



Distribution, 9 species. Lower Silurian. North America. 



EiCBTWAXDiA, Billings, 1858. 



Dedicated to Professor Eichwald, the celebrated Eussian 

 palaeontologist. 



Type, E. subtrigonalis. Lower Silurian. Canada. 



Shell with the ventral valve perforated on the umbo for the 

 passage of a peduncle ; the place of the foramen beneath the 

 beak being occupied by an imperforate concave plate ; the in- 

 terior 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 Camorophoria. 



Distribution, 3 species. Silurian, Canada ; England. 



Stricexajstdd^ia, Billings, 1863. 

 Dedicated to the late Professor H. E. Strickland. 

 Synonyms, Stricklandia, Billings, 1859 (non Buckman) ; 

 Ronsselseria (pars), Hall. 



• See p. ?75. 



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