74 University Geological Survey of Kansas. 



Bronson, Bourbon county, Kansas City, Buffalo Mound, Wa- 

 baunsee county. 



This species is easily distinguished by its deep mesial sinus 

 and strong bilobate appearance, together with a long hinge. 



PRODUCTUS. 



Sowerby, Min. Con., I, p. 153, (1814). 



de Koninck, Recher. Anim. Foss., I, p. 11, (1847). 



Hall, 29th Rep. N. Y. St. Cab. Nat. Hist., p. 245 (1867) ; Pal. N. Y., IV, p. 146, (1867). 



Hall and Clarke, Pal. N. Y., VIII, pt. I, p. 321, (1892) ; 11th Ann. Rep. N. Y. St. Geol., p. 297, (1894). 



This genus has been divided into groups, as follows : 



Group I. Lineati Waagen. " Surface covered with fine radi- 

 ating costse which are rarely spinous and are not crossed by 

 concentric plications or wrinkles. The shells are greatly pro- 

 duced and sometimes the anterior margins of the shells are 

 modified by the development of a fold or sinus. The shells 

 were very fragile and have usually been subject to much dis- 

 tortion in fossilization." 4 



Group II. Irregulares Waagen. "Elongate shells very nar- 

 row at the beak, mytiliform in outline ; mode of growth quite 

 irregular. Surface as in the Lineati; spines grouped almost 

 wholly about the cardinal line." 4 



Group III. Semireticulati de Verneuil. "The longitudinal 

 ribs are sparsely spinous ; surface of visceral disc covered with 

 concentric wrinkles." 4 



Group IV. Spinosi de Verneuil. " Surface strongly tubercu- 

 lose or spinous ; not reticulated." 4 



Group V. Fimbriati de Koninck. "Surface without radiate 

 strict or ribs ; covered with concentric ridges or plications, 

 bearing rows of small thickly set spines." 4 



Group VI. Horridi de Verneuil. "Surface without concen- 

 tric or radiating plications ; pedicle valve with a deep sinus." 4 



Group VII. Mesolobi de Koninck. " Surface without radiat- 

 ing or concentric plications except a prominent median rib." 4 



All of our Kansas species come in groups I, III, IV, and V. 



I. — Lineati: P. cora and its varieties. 

 III. — Semireticulati: P. semireticulatus, costatus, pcrtcnuis, longispinus. 



IV. — Spinosi: P. nebraxcensis. 



V. — Fimbriati: P. punctatus, symmetricus. 



4. Hall and Clarke, Pal. N. Y„ VIII, I, p. 326. 



