Weller — Kinderhook Fauna! Studies. 197 



angle; both valves regularly and nearly equally convex ; bra- 

 chial beak closely incurved beneath the pedicle beak, which 

 is slightly incurved. Foramen and delthyrium unknown. 

 Surface marked by from sixteen to eighteen distinct some- 

 what rounded plications on each valve, which mostly reach 

 the beak with some distinctness, but are occasionally increased 

 both by implantation and bifurcation. They are traversed by 

 fine radiating lines, and crossed by fine concentric lines of 

 growth." 



** Mesial fold and sinus scarcely defined, but the front is 

 slightly emarginate in the older specimens, by the elevation 

 of the lingual extension of the lower pedicle valve with a 

 gradual curve, which includes five or six of the plications." 



The dimensions of the type specimen are: length 43 mm., 

 breadth 39 mm., and thickness 27 mm. 



Hetnarks. The geologic horizon of this species is recorded 

 by its original author as '* base of the Burlington Limestone," 

 but the specimens indicated as types in the University of 

 Michigan collection include as well individuals from the mag- 

 nesian layer at the top of the Kinderhook. These lower 

 specimens, however, are all more or less imperfectly pre- 

 served, though they apparently belong to the sanie species as 

 the more perfect Burlington limestone specimens. Among 

 the accompanying illustrations of this species, figures I, 2 

 and 3 are views of a nearly perfect individual from the Bur- 

 lington limestone, which may be taken as the true type 

 of the species. Figure 4 is one of the most perfect of the 

 magnesian limestone specimens. The shell illustrated by 

 Keyes (Mo. Geol. Surv., Vol. V., Paleontology II. pi. 41, 

 Fig. 11), under the name Rhynchonella sp. f is quite cer-^ 

 tainly an individual of this species. 



Camarotoechia persinuata (Win.). 



PL XIX. f. 6. 



Rhynchonella persinuata, Bull. U. S. G. S. 153: 534. 



Original description. *' Shell of medium size, transversely 

 oval, with abbreviated rostral extension. Cardinal slopes 

 nearly straight, sides rounded, front straight. Pedicle valve 

 depressed, with about twenty straight plications, of which 

 eight occupy the broad and rather shallow sinus. Anterior 



