48 Transactions of the Academy of Science of St. Louts 
ATRYPA DEVONIANA WEBSTER, FENTON & FENTON 
Plate 3, figs. 1—5 
Atrypa devoniana Webster, 1921. American Midland Naturalist, 
Vol. 7, p. 19. 
Artypa devoniana Webster, Fenton & Fenton, 1924. Michigan 
Univ. Cont. Museum of Geol. Vol. 1, p. 134, pl. 26, figs. 16—24. 
Artypa devoniana Webster, Fenton & Fenton, 1932 American 
Midland Naturalist, Vol. 13, pl. 21, fig. 5. 
In Missouri, Atrypa devoniana occurs only in the gray, soit, 
sandy upper member of the Snyder Creek Shale, associated wit 
Atrypa snyderensis Greger, Cyrtina triguetra Hall, Productella 
callawayensis Swallow, and a large species of Spirifer commonly 
referred to S. euryteines Owen. 
Branson has figured a specimen of A. devoniana as A. rett- 
cularsis, Mo. Geol. Survey, Vol 17, pl. 23, fig. 12, the shell im 
question coming from the upper beds of the Snyder Creek shale. 
The Snyder Creek specimens before me are identical with 
a series of this species from the Hackberry Grove locality im 
Iowa. Along with the fine striae—9 in the space of 5 mm.—the 
narrow, deep U shaped sinus is an outstanding character. 
Average measurements of twenty mature specimens of A. 
devoniana trom the Snyder Creek shale of Missouri is as fol- 
lows—length 20 mm., breadth 22.5 mm., thickness 13 mm. 
ATRYPA ROCKFORDENSIS FENTON & FENTON 
Plate 3, figs. 6, 7, 8. 
Altrypa rockfordensis, Fenton & Fenton, 1924. Michigan Univ. 
Cont. Mus. Geol., Vol. 1, p. 142, pl. 27, figs. 4—12. 
Atrypa rockfordensis is not abundant in the Snyder Creek 
shale. However, in a zone of almost 4 inches, near the base of 
the upper third of the shale, it is found in numbers, but only 
as separated valves. It first appears in the Snyder Creek in a 
thin yellow to brown layer, directly above the crinoidal limy shale 
member and is associated with Stropheodonta navalis Swallow, 
