PENTAMERIDiE OF LOWER DEVONIAN AGE. 
381 
Gypidula lieviiisciila (n. s.). 
PLATE LVIII. 
Shell varying from subcircular to broadly ovoid, gibbous in the young 
state, becoming ventricose. 
Ventral valve, in the young shell, regularly convex, with beak abruptly 
pointed and neatly incurved, becoming more gibbous or ventricose as 
the shell increases in size, with the umbo prominent and beak arcuate ; 
regularly curving to the sides and front, without mesial sinus or 
elevation. 
Dorsal valve regularly convex in young shells; old shells more gibbous 
above, and becoming broadly depressed towards the front, without 
distinct sinus. Area distinct; beak scarcely incurved. 
Surface smooth or marked by concentric striae, which are slightly undu¬ 
lated towards the front of the shell; and in a large specimen, the 
exfoliated surface is obscurely marked by fine striae. 
The young specimens of this species have much the aspect of Nucleo- 
spira ; but when the cardinal line is visible, there is a conspicuous trian¬ 
gular fissure with a flattened space on each side. This feature is 
sometimes quite marked in the separated ventral valve. The spoon¬ 
shaped pit is comparatively wide and deep, and supported on a short 
septum. In the dorsal valve the lamellae are divergent from their origin. 
The largest specimen before me has a length of seven-eighths of an 
inch, with a slightly greater width. 
Geological formation and locality. Collected from strata of Devonian age, at 
Waterloo, Iowa, by Mr. O. St. John, to whom I am indebted for the specimens. 
