84 BULLETIN OF THE LABORATORIES 



rather distant concentric strioe and posteriorly by thread-like elevated 

 radiating stride. In general appearance this shell is very like Maci'o- 

 don delicatus of the coal-measures, but differs from all species of Macro- 

 don or Parallelodon in having the greatest length near the ventral line 

 and the lower angles extended and acute. The markings distinguish 

 it from any species of Area of the Waverly. Length 18 mm; height 

 nearly 8 mm ; beak distant from anterior about 6 mm. Other broken 

 specimens indicate that this species reaches a considerably greater 

 size and that the entire surface, when preserved is covered by the fine 

 but distinct radiating thread-like striae. 



Genus Gonoidon, Gen. n. 

 ( Gonia, an angle ; odotis, a tooth. ) 



This name is proposed with some hesitation to receive a nuculi- 

 form shell seeming to differ in hinge structure from any genus of the 

 Palaeozoic era. 



Shell equivalve, very unequilateral, gibbous, not gaping ; resem- 

 bling Palaeoneilo, but the hinge is continuous, slightly flexed beneath 

 the beaks, without true teeth, (.'*) but the hinge margin of both valves _ 

 zig-zagged by sharp incisions into which corresponding projections of 

 the opposite valve fit closely. The series of denticulations thus formed 

 is continuous, but the size of the excisions diminishes before and be- 

 hind the beaks. Posterior adductor scar nearly 'erminal. 



Gonlodoih ohioensis, sp- "• 

 (Plate XII, Figs. 23, 24, 25.) 



Shell closely resembling Palaeoneilo; of medium size, very tumid, 

 umbo prominent, incurved. The outline is oblong-elliptical, lower 

 margin nearly straight, posterior extremity rather acutely rounded, 

 anterior extremity short, abruptly rounded; hinge-line equal to 

 nearly two-thirds the entire length, about twelve angulations behind 

 the beak and six to eight in front; ligament -apparently below the 

 beaks> not disturbing the continuity of the series of angulations. The 

 greatest convexity is near the umbo. Surface marked by fine reg- 



