The interior is marked by large, double, profoundly deep 

 muscular impressions; the principal scars are abruptly de- 

 pressed on the inner margins, the minor scars faintly marked 

 except on old individuals. The hinge plates are of medium 

 width and contain about eight or ten slightly curved teeth on 

 the anterior side of the beak, and from twelve to fourteen on 

 the posterior side; beaks (in the cast) rather distant. The 

 Internal cavity of the shell is deep. 



This species somewhat resembles T. contraeta (Ctenodonta 

 eontracta, Salter, Canadian Organic Remains, Decade I, pi. 8, 

 fig. 4 and 5); but differs in the greater proportional length, 

 greater breadth of the anterior end, and greater obliquity of 

 the posterior elope. The shell is more ventricose, the beaks 

 nearest to the posterior end (instead of the anterior) and the 

 muscular impressions more deeply marked. 



Geological Formation and Locality. In rocks of the age of 

 the Trenton limestone group ; the buff limestone, at Beloit, 

 Janesville and Mineral Point, Wisconsin ; at Dubuque, Iowa, 

 the Falls of St. Anthony, and other places. 



Collectors. Prof. Nason, E. Hobart and James Hall. 

 TELLINOMYA OVATA, (n. s.) 



description. Shell ventricose, sub-ovate; cardinal line straight 

 or very little curved; anterior and broad, obliquely truncate; 

 posterior end short, narrow ; basal margin broad rounded, a line 

 drawn from its junction with the anterior and posterior slopes 

 passes across the middle of the shell; beaks small, not promi- 

 nent, curved, directed towards the anterior end. Valves gibbous 

 at the anterior and attenuate at the posterior end ; the length, 

 breadth and thickness of the valves when compared are seven, 

 six and five. Surface of shell smooth or marked by a few con- 

 centric lines of growth of moderate strength. 



This species resembles T. nasuta; but the beaks are more 

 nearly central, and the posterior end is not produced in 

 the same manner. The basal line is regularly curved and does 

 not show the contraction on the posterior side of the middle of 

 the base which is observed in that species. 



Geological Formation and Locality. In the Trenton group, 

 (Buff limestone,) Beloit, Wisconsin. 



Collector. Edward Daniels. 



