Atrypae of the Central Missouri Devonian 43 
Atrypae of the Central 
Missouri Devonian 
D. K. Grecer 
ABSTRACT, 
This paper is offered with a view to giving a definite value 
to the various species of Atrypa found in the Devonian of 
Central Missouri, 
Throughout the many reports of the Missouri Geological 
Survey, and elsewhere, the forms herein described are referred 
to as Atrypa reticularis, Atrypa sp., etc. 
Six species are recognized from the Central Missouri Devon- 
ian, three of which were orginally described from Iowa, two are 
here figured and defined as new species and the sixth—Aftrypa 
Missouriensis Miller, orginally described from immature speci- 
mens, is fully illustrated and its horizon definitely established. 
ATRYPA MISSOURIENSIS MILLER 
Plate 1, figs. 1—16. 
Plate 2, figs. 1—6. : 
Atrypa missouriensis S. A. Miller, Indiana Dept. Geol. Nat. 
Res., 18th Rept. (Adv. sheets), p. 61, pl. 9, figs. 19—21. 
Atrypa missouriensis S. A. Miller, Indiana Dept. Geol. Nat. 
Res., 18th Rept., p. 315, pl. 9, figs. 19—21, 1894. 
Atrypa missouriensis Miller, Fenton and Fenton. American Mid- 
land Naturalist, Vol. 12, No. 1, 1930, p. 15, pl. 2, figs. 5—9. 
OricinaL Description, “Shell small, subcircular, rather 
longer than wide, valves very moderately and nearly equally 
convex, cardinal extremities rounded. 
_ Ventral valve most convex in the umbonal region, which 
1S rather sharply rounded transversely, from which elevation the 
shell gently slopes to the front and the antero-lateral sides. Beak 
Projects a little beyond the beak of the opposite valve, but is 
not incurved over it, 
“Dorsal valve rather more evenly convex that the ventral, 
