Fauna of the Morrow Group 
243 
section and deeply embracing, indented to nearly half their 
height by the preceding whorls; height of whorl about two- 
thirds its breadth and about two-fifths the total diameter of 
the shell; umbilicus comparatively wide; surface of the shell 
not marked ,by ribs, but with rounded constrictions crossing 
the venter and lateral slopes in the mature portion of the shell, 
about five constrictions in a volution. 
Dimensions. 
Diameter 23.9 mm. 
Height of last whorl 9.5 mm. 
Width of umbilicus 8.4 mm. 
Breadth 12.3 mm. 
Height of last whorl from top of preceding 5.2 mm. 
The specimen shows about five whorls at the diameter of 23.9 mm. 
The sutures consist of three pairs of external lobes and as 
many saddles ; the siphonal lobes are long, narrow, and pointed ; 
first lateral pair broader and slightly pointed, and on the um- 
bilical shoulder is a very shallow, broadly V-shaped lobe; 
siphonal saddle narrow, indented at the end ; first lateral saddle 
nearly twice as high and broadly rounded ; second lateral saddle 
not so high as first and more narrowly rounded. The inner 
lobes are three in number : a long, narrow, pointed, antisiphonal 
lobe with a shorter lobe of about the same shape on either side ; 
the four internal saddles are rounded, the lateral ones very broad 
and the mesial pair quite narrow. 
Horizon and locality. Kessler limestone : East Mountain, 
Fayetteville, Arkansas (Station 209). Morrow formation: near 
Choteau, Oklahoma (Station 302), 
Gastrioceras pygmaeum n. sp. 
• Plate XVI y figures 11-1 lb. 
Description. Shell small, discoidal to sub-globose, moderately 
involute, whorls semi-lunular in cross-section and deeply em- 
bracing, indented to nearly half their height by the preceding 
whorls ; breadth of whorl nearly one-fourth greater than its 
height and equal to about one-half the diameter of the shell; 
umbilicus comparatively large, its width slightly greater than 
one-third the diameter of the shell; surface bearing numerous 
faint ribs confined to the rounded umbilical shoulder and obso- 
