STE. GENEVIEVE MARLS NEAR PORT DODGE G15 



specimen measures: length 14.5 mm., greatest width 15 mm., 

 thickness 8.8 nun. 



Pedicle valve convex, greatest convexity over the posterior 

 half, mesial sinus beginning on the umbo whence it continues as 

 a shallow groove to the anterior third of the valve where it be- 

 comes deeper and wider and extends forward in a tongue-shaped 

 point ; beak incurved over that of the opposite valve and termin- 

 ating in a large round foot opening ; no cardinal area. 



Brachial valve convex, mesial part strongly elevated in front 

 and the elevation set off by a marked depression on each side; a 

 shallow median gTOove occurs along the summit of the fold in the 

 larger shells; beak curved snugly beneath that of the opposite 

 valve. 



Surface of the valves smooth except for crowded concentric; 

 lines of growth towards the front margin. 



This variable shell has passed under several names in the Iowa 

 Reports. It is doubtless the shell denoted as AtJiyris amhigua, 

 — see reference earlier in this paper. Its usual name, however, 

 has been Athyris or 8eminula siob quadrat a^ each of which is a 

 synonym of the name now recognized. 



Occurrence. — Ste. Genevieve, Pella beds, along Lizard creek 

 and in the Illinois Central railroad cutting, Webster county; 

 Iowa. 



TRILOBITES. 



Phillipsia (species undetermined) 



Plate XII, fig. 35. 



A single small and imperfect pygidium was collected by Doc- 

 tor Lees in the marl on North Lizard creek. The margin of th'? 

 specimen is broken away. The axis is prominent and is dis- 

 tinctly set off from the lateral lobes ; thirteen segments are pre- 

 served, a number at the distal end being lost. All the segments 

 are sharply defined by narrow, deep sulci. The segments of the 

 lateral lobes are wider than those of the axis, six of the latter be 

 ing a little wider than five of the former. 



Occnrrence. — Ste. Genevieve, Pella beds, along north branch 

 of Lizard creek, Webster county, Iowa. 



ADDENDUM. 



Since the foregoing paper was written an exposure of the 

 Ste. Genevieve marls has been found in the northwest quarter 

 of section 6, Cooper township, in a small ravine on the east 



