612 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



cases approachinf^ the character of wrinkles, best developed on 

 the anterior part of the valves. Minute concentric markings may 

 be seen with a lens, especially between the costae where they have 

 been protected from wear. 



Many fragments of this fine species were collected but whole 

 specimens are rare. The best specimen, figur3S 21 and 22 of the 

 plate, was collected by Charles Rubenstein. Many of the shells 

 exhibit boring of ClionoUthes lizarderisis and in some cases their 

 broken condition is due to the ravages of this little boring sponge. 



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

 Webster county, Iowa. 



Pugnaides ottumwa (White) 



Plate XII, figs. 1-11. 



1914. Pugnaides ottumwa Weller, Geol. Surv. 111., Mono'i". I, p. 



193, pi. XXV, figs. 7-17. 



Shell small, five-sided in outline, width and length about equal. 

 Dimensions of an average specimen are : length 12 mm., width 11 

 mm., thickness 7 mm. 



Pedicle valve sharply pointed at the beak, umbo strongly eon- 

 vex, mesial sinus confined to the anterior part of the valve where 

 it is broad and relatively deep; anterior margin sinuous due to 

 the extension of the mesial part of the valve ; beak incurved, 

 produced 1 to 1.5 mm. beyond the brachial valve ; delthyrium tri- 

 angular, partly closed; foramen round, terminal, size and posi- 

 tion variable when a series of shells is examined ; plications sim- 

 ple and limited to the anterior half of the valve, one to three 

 (rarely four or five) in the bottom of the sinus and from three 

 to five on each slope. 



Brachial valve more convex than the pedicle; mesial fold con- 

 fined to the anterior part of the valve and strongly elevated in 

 front; beak incurved beneath that of the pedicle ; arrangement of 

 the plications as on the opposite valve. . 



Surface of both valves smooth except for the plications and a 

 few growth lines near the anterior margins. 



This species is very abundant at all the localities where fossils 

 are obtained. It is especially characteristic of the Pella beds and 

 is regarded as their index fossil. It is found also at Ottumwa 

 (whence the specific name), Pella, Oskaloosa, Kecsauqua, and 

 elsewhere in southeastern Iowa. 



