BRACHIOPODA. 61 



fauna of Square Lake, Maine. Of the foregoing species we know the character 

 of the loop in Whitjiddella cylindrica, W. nitida and W. intermedia. 



The forms of Whitfieldella cylindrica occurring in the Niagara limestone at 

 Hillsboro, Ohio, have a remarkably elongate shape, broad and abrupt cardinal 

 slopes on the pedicle-valve, subnasute anterior extremity. In these respects 

 the species differs from other members of the group, but the character of its 

 loop as developed from a solid internal cast in silica, requires, for the present, 

 its retention in this association. 



A very similar species in all external characters is Dalman's Alrypn prunum, 

 from an equivalent horizon in Gotland 



Genus HYATTELLA, gen. nov. 



PLATE XLVni. 



This term is introduced for a group represented by the peculiar species, 

 Atrypa congesta, Conrad, of the fauna of the Clinton group. 



This species has been found to po.ssess a loop like 

 that of Whitfieldella, but presents some significant 

 points of variation from tliat genus in other re- 

 spects, viz. : 



"^ Fig. 45. The loop of Byattella 



The form is compactly subpentahedral ; the umbo cmgesta.iuM. {<■.) 



of the pedicle-valve acute, concealing most of the deltidium. The pedicle- 

 valve bears a strong median sinus and two faint lateral sinuses, the opposite 

 valve having corresponding folds. The surfoce of the shell and the ante-lateral 

 margins are strikingly sinuate. Fine, sharp, closely crowded concentric strioe 

 cover the exterior. The interior of the pedicle-valve has a deep and strongly 

 striate pedicle-cavity, Ijounded by strong dental lamelte ; the diductor scars 

 are distinctly defined, enclosing a linear adductor. In the brachial valve the 

 hinge-plate is triangular and divided medially by a deep cleft. The lateral 

 portions are broad and elevated, supporting short, straight crura. The spiral 

 ribbon makes not more than six volutions, forming very loose coils. There 

 is no median septum. 



