LAMELLIBEANCHS. 119 



area broad with well-defined farrows. Surface marked by fine 

 concentric lines of growth and imbricated lamellae. 



Horizon and localities. Upper Carboniferous, Upper 

 Coal Measures : Kansas City. 



Myalina swallovi MCCHESNEY. 



Plate xllii, figs. 3a-c. 



Myalina swallovi McChesney, 1859 : Desc. New Species Foss., p. 57. 

 Myalina swallovi Meek & Worthen, 1866: Geol. Sur. Illinois, vol. II, p. 



341, pi. xxvii, fig 1. 

 Myalina swallovi McChesney, 1867 : Trans. Chicago A cad. Set.,, vol. I, 



p. 4, pi. ii, fig 6. 

 Ancella hausmanni Geinitz, 1866 : Garb und Dyas in Nebraska, p. 25, tab. 



ii, fig. 8. ( Not Qoldfuss, 1834.) 

 Myalina? swallovi Meek, 1875: U. S. Geol. Sur. Nebraska, p. 201, pi. 



ix, figs. 7a-b. 

 Myalina? swallovi White, 1884: Geol. Sur. Indiana, Report for 1883, p. 



141, pi. xxx, figs. 6, 7, 8. 

 Myalina swallovi Keyes, 1888: Proc. Acad. Nat. Sci., Phila., p. 232. 



Shell rather small, nearly or quite equivalve, modioliform 

 or mytiloid, convex, or even subangular, along the umbonal 

 slopes from the beaks to the anterior basal margin ; posterior 

 and postero-dorsal regions cuneate ; cardinal border nearly 

 straight, and about one-half the length of the valves, passing 

 almost imperceptibly, or without any angularity, into the pos- 

 terior margin, which rounds down with a semicircular curve to 

 the narrowly rounded basal extremity; antero-basal border 

 ascending obliquely forward, more or less sinuous near the 

 middle, or sometimes a little above, usually swelling out into a 

 kind of lobe or protuberance above the middle in front of the 

 umbonal slope. This prominence sometimes extends a little 

 beyond the beaks and varies more or less in breadth. Beaks 

 small, very oblique, not projecting beyond the cardinal margin, 

 and located so near the anterior extremity as often to appear 

 very nearly terminal. Surface rather smooth, but showing fine 

 concentric lines, which in well-preserved specimens are some- 

 times crossed by very fine, obscure traces of radiating stria- 

 tions that curve upward on the posterior dorsal region. ( Meek.) 



Horizon and localities Upper Carboniferous, Lower 

 Coal Measures : Carbonier ( Saint Louis county ) ; Upper Coal 

 Measures : Richmond ( Ray county), Kansas City. 



