58 Brachiopoda of the Cincinnati Group. 



impressions with very prominent boundaries all round, eacli one oblong, 

 depressed, and nearly smooth in the middle, or subquadrate, slightly 

 longer than wide ; the two together transversely oblong, one third 

 wider than long, the width equaling the length of the valve ; the two 

 prominent inner boundaries leave a deep sulcus between them, at the 

 anterior end of which only a very short mesial septum is developed, 

 not reaching nearly to the beak ; interior of the muscular impression 

 nearly smooth, each divided by a faint diagonal ridge ; the space 

 immediately in front of the impressions coarsely pitted and marked 

 with a few obscure, branching impressions of pallial vessels, none of 

 which are visible on the deflected front; cardinal angles irregularly 

 punctured, and with minute wrinkles. Width, eight lines ; proportional 

 length of receiving valve, iVo^^^s inch; of entering valve, rVo^^^ 

 inch; depth of entering valve, j^^o^pths inch; depth of receiving valve, 

 ,Yoths inch. 

 Its range is co-extensive with the Cincinnati Group. 



Family Sphiferidce. 



Shell free, inequivalve, varying greatly in form and ornamentation, 

 according to the genera and species ; with or without a cardinal area ; 

 oval appendages large, provided with calcified, ribbon-shaped sui)ports, 

 which are spirally coiled, so as to form two cones, the apices of which 

 are directed outward toward the lateral margins of the valves ; shell 

 structure fibrous or fibro-punctate. 



Animal unknown; apparently sometimes attached by a muscular 

 peduncle. 



This family includes Zygospira and Tremafospira, with other genera. 



Genus Zijgospira — (Hall). 



Shells bivalve, equilateral, inequivalve ; surfiices plicate in the 

 typical species ; a sinus on the dorsal valve. Internal spires arranged 

 somewhat as in Atrypa, with a broad loop passing from the outer limbs 

 of the spiral band entirely across, from side to side, near to or above 

 the center, and close to the inner side of the dorsal valve. 



(Z. modeda, typical sp.) 



Zygospira modesta — (Say). 



Shell small, suborbicular or plano-convex, sometimes a little wider 

 than long; posterior lateral margins converging to the beaks at an 

 obtuse angle ; lateral margins rounded to the front, which is sometimes 

 straight or slightly sinuous. 



