PELECYPODA. 149 



Description — Shell of medium size, hinge line usually slightly shorter than the 

 greatest width of the shell. The dimensions of three specimens are: Width, 11.5 mm. t 



14 mm., 18 mm.; length of brachial valve, 7 mm., , — — ; length of pedicle valve, 



11 mm., 12 mm., 20 mm.; height of cardinal area, 4.5 mm., ., 6.5 mm. 



Pedicle valve with strongly curved cardinal area. Surface marked by six or seven 

 rounded plications on either side of the sinus; no plications in the sinus; the plications 

 extending only about half the length of the valve. The medium septum extends 8/11 

 of the length of the valve. 



Brachial valve moderately convex, with a narrow well defined fold. No plica- 

 tions on the fold, six or seven plications on either side of the fold. The plications ex- 

 tend only about half the length of the shell. A median septum extends more than half 

 the length of the valve. 



All of the specimens examined are internal moulds. 



Occurrence — Sandy phase of the St. Laurent limestone, Little Saline Creek, Ste. 

 Genevieve County. 



< 

 Cyrttna hamiltonensts Hall 



Description and synonomy on pages 106 and 107. 



Specimens are figured on plate 19. 

 Specimens of the ordinary kind occur in the St. Laurent limestone, 3 miles south 

 of St. Marys. 



Family Athyridae 



Genus Athyris McCoy 



Athyris fultonensis? (Swallow) 



Description and synonomy on pages 109 and 110. 



Figures on plate 17. 



Remarks — The great variety in this species and the lack of diagnostic characters 

 make it easy to find large numbers of varieties. Only two specimens from southeastern 

 Missouri are in the Walker Museum collections. They are small and quite different 

 from each other. They resemble A. fultonensis (Swallow) but the smaller specimen 

 has more distinct fold and sinus than typical small A. fultonensis. 



Occurrence — Grand Tower limestone of Little Saline Creek. 



MOLLUSCA 



Class PELECYPODA 



Order Prionodesmacea 

 Super-family Pteriacea 



Family Pterineidae 

 Genus Pterinea Goldfuss 



Pterinea flabellum (Conrad) 



Plate 36, figure 2. 

 1842. Avicula flabella Conrad, Jour. Acad. Nat. Sci., Phila., vol. 8, pi. 238, pi. 12, 



fig. 8. 

 1884. Pterinea flabella Hall, Pal. New York, vol. V, pt. 1, Lamellibranchiata, I, pp. 



93-96, pi. 14, figs. 1-21; pi. 15, figs. 1, 4-6, 8-10; pi. 83, figs. 11, 12. 



