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BULLETIN OF THE LABORATORIES 
rather distant concentric striae and posteriorly by thread-like elevated 
radiating striae. In general appearance this shell is very like Macro- 
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 i8 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. 
i 0 
Genus Gonojdon, Gen. n. 
( Gonia, an angle ; odous, 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 Pal^oneilo, 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 terminal. 
Goniodon ohioensis, sp. n. 
(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- 
