BRACHIOPODA. 



Pamily III . — Ehynchonellidje. * 

 Eatonia, Hall, 1859. 



Dedicated to the late Professor Amos Eaton. 



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



Shell like tliat of Rhynchonella ; tlie iower haK of the ventral 

 valve witli a broad deep sinns. 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 lameUse surround- 

 in.g the muscular impression, which is much stronger and differs 

 in some respects from that of Rhynchonella. 



Fossil, 7 species. Dpper Silurian. United States. 



Camerella, BiUings, 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 Fentamerus. 

 Dorsal valve with a single mesial septum and two short lamellae 

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

 Surface smooth or obscurely plicated. 



Distribution, 9 species. Lower Silurian. North America. 



EiCHWALDiA, BiUings, 1858. 



Dedicated to Professor Eichwald, the celebrated Bussian 

 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 Gamorophoria. 



Distribution, 3 species. Silurian, Canada ; England, 



STRiCEXANDDsriA, Billings, 1863. 

 Dedicated to the late Professor H. E. Strickland. 

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

 Eensselseria (pars), Hall. 



* See p. 375. 



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