336 EIGHTEENTH REPORT ON THE STATE CABINET. 



CONCHIFERA (=ACEPHALA). 



The following species, including several heretofore described, have been 

 recognised in the Niagara limestone of Wisconsin and adjacent parts of 

 Illinois. 



GENUS AMBONYCHIA (Hall). 



AMBONYCHIA APH^^A (n. s.). 



Shell somewhat obliquely ovate ; anterior side broadly rounded ; beak in 

 the cast acute ; hinge-line straight, and about half the length of the 

 shell. The posterior basal extremity is somewht adJuptly rounded. Mus- 

 cular impressions large, situated below the centre of the length of the 

 shell. 



The greatest width of the shell is equal to about two-thirds the length. 

 One specimen measures one inch and seven-eighths in length and one 

 inch and a quarter in width. Other specimens are smaller than the one 

 measured. 

 This species is proportionally broader and shorter, with the beaks less 



extended than E. acutirostra from the same horizon. 



Formation and locality. In limestone of the age of the Niagara group, 



at Wauwatosa, Wisconsin, and Bridgeport, Illinois. 



AMBONYCHIA ACUTIROSTEA. 



Amhonychia acutirostra : Hall, Annual Report of Progress Geol. Survey of "Wis- 

 consin, 1860. 



This species is proportionally longer than the preceding, less expanded 

 on the anterior margin, and has the beaks elongate and attenuate. In 

 many respects it resembles the Myalina mytiliformis of the grey sand- 

 stone of the Clinton group. The species occurs at Wauwatosa and Racine, 

 Wisconsin. 



These species are probably not true Ambonychia, but m the condition 

 in which they occur, we have not sufficient characters remaining, to author- 

 ize their separation. 



Formation and locality. In limestone of the age of the Niagara group, 

 near Milwaukee, Wisconsin. 



GENUS AYICULA (Klein). 



AYICULA UNDATA. 



A vicula undata: Hall, Palaeontology of New York, Vol. ii, pa. 280, pi. 59, f. 2. 



A specimen from Racine, Wisconsin, and another from Bridgeport, 



Illinois, resemble this species from the Niagara group of New- York. 

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