American Scientific Association. 301 



vicinity, but from another locality in the Laurentian formation, 

 Mr. John McMullin, one of the explorers of the Geological Survey 

 had obtained specimens well worthy of attention. They consisted 

 of parallel or apparently concentric layers resembling those of the 

 coral Stromatocerium, except that they anistomoze at various 

 parts, the layers consist of crystaiine pyroxene, while the 

 interstices are filled with crystalized carbonate of lime. These 

 specimens had recalled to recollection others which had been 

 obtained from Dr. Wilson of Perth some years ago, and had not 

 then been regarded with sufficient attention. In these similar 

 forms are composed of green serpentine, concretionary while the 

 interstices are rilled with white dolomite. If it be supposed that 

 both are the result of mere unaided mineral arrangement, it would 

 seem strange that identical forms should result from such different 

 minerals in places so far apart. If the specimens had been 

 obtained from the altered rocks of the Lower Silurian series, there 

 would have been little hesitation in pronouncing them to be fossils. 

 The resemblance of these forms to Stromat^cerium from the Birds- 

 eye limestone, when the coral has been replaced by concretionary 

 silica is very striking. In the pyroxenic specimens, the pyroxene 

 and the carbonate of lime being both white, the forms although 

 weathered into strong relief on the surface, are not perceptible in 

 fiesh fractures until the fragments are subjected to an acid, the 

 application of which shows the structure running throughoti thet 

 mass. Several specimens of these supposed fossils were exhibited to 

 the Section. 



ART. XXIII. — Description of a new Genus of Brachiopoda, 

 and on the Genus Cyrtodonta. By E. Billings. 



(From Report of Geological Survey, 1858 and '59, unpublished.) 



Genus Camerella, Billings. 



Generic characters. — Family Rhynconellidae ; 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 lamellae for the support of the 

 oral appendages, as in Rhynconella. 



Camerella Volborthi, Billings. 



Description. — Small, nearly globular; ventral valve, with a 

 broad mesial sinus which deeply indents the opposite valve, but 



