$2 Transactions of the Academy of Science of St. Louts 
Schizophoria macfarlaini Meek, Spirifer amarus Swallow, Pro- 
ductella marquessi Rowley, Cranaena morsii Greger, Athyris 
minima Swallow, Strophonella crassa Rowley, many Stropheo- 
dontas, Bryozoans and Corals. 
ATRYPA SNYDERENSIS SP. NOV. 
Plate 4, figs. 1—5. 
Shell of medium size for the genus, sub-circular to ovoid 
in outline, biconvex, length and width almost equal. Hinge line 
less than the width of the shell. Cardinal extremities rounded. 
Brachial valve ventricose, frequently quite gibbous, its greatest 
convexity at or directly forward of the umbo. 
The surface is ornamented by strong, rounded or sub-angular 
plications which are increased by bifurcation and implantation, 
crossed by lamellose, imbricating concentric lines of growth. 
These lamellar growths are extravagantly developed in most 
individuals, frequently equaling, and occasionally surpassing, the 
length of the valves proper. Figure 5, pl. 4 shows an artificial 
preparation in which all but the marginal lamella has been re- 
moved, revealing the shape and size of the shell. 
The lamellae are very thin (0.3 mm.), continuous, fluted 
plates and do not coelace one with another. They frequently 
bifurcate along the outer edge and in rare instances implantation 
occurs, simulating the surface of the underlying shell surface. 
Measuremens of a series of specimens divested of their ex- 
travagantly developed “frills” average: length 31 mm., breadth 
30mm., thickness 17 mm. 
The largest specimen of. this species in our collection—length 
and breadth 85mm. with the growth varices removed, measures: 
length 36 mm., breadth 35 mm. Figures 5 pl. 4 shows a specimen 
with all but the marginal fringe removed. 
Atrypa snyderensis is found only in the Upper Snyder Creek ; 
it is always associated with the following species: Spirifer 
euryteines, Productella callawayensis, Cyrtina triquetra, Strop- 
peodonta callawayensis, Stropheodonta quadrata, and many 
internal casts of Pelecypods, ~ 
