ALLORISMA. 417 



Mtacites, Woodward, 1856. Manual Mollusca, p. 496. 



Allorisma, Shumard and Swallow, 1858. Trans. Acad. Sci. St. Louis, vol. i> 



p. 210. 



— Meek and Hayden, 1858. Proc. Acad. Nat. Sci. Pliilad., p. 263. 



— M'Chesney, 1859. Trans. Chicago Acad. Nat. Sci., vol. i, p. 56. 



— Eichivald, 1860. Lethaea Rossica, p. 1037. 



— Swallow, 1860. Trans. Acad. Sci. St. Louis, vol. i, p. 656. 

 Mtacites, Salter, 1801. Mem. Geol. Surv. Gt. Brit., Iron Ores, pt. 3, p. 221. 

 Allorisma, Meeh and Hayden, 1865. Smithsonian Contrib. Knowl. Pal. Upper 



Missouri, vol. xiv, p. 36. 



— — 1868. Geol. Surv. Illinois, vol. iii, p. 538. 



— Swallow, 1868. Trans. Acad. Nat. Sci. St. Louis, vol. ii, p. 95. 



— Meeh and Worthen, 1869. Proc. Acad. Nat. Sci. Philadelphia, p. 171. 



— Meek, 1871. Ibid., p. 167. 



— Hayden, 1872. Final Rep. U.S. Geol. Surv. Nebraska, p. 221. 

 Non — Meek and Worthen, 1873. Geol. Surv. Illinois, vol. v, p. 585. 



— White, 1875. Rep. Geog. and Geol. Exp. and Surv. W. of 100 Merid , 



pt. 1, vol. iv, p. 155. 



Non — Meek, 1875. Rep. Geol. Surv. Ohio Pal., vol. ii, pt. 2, pp. 309, 311, 



312, and 344. 



— F. Earner, 1870. Lethsea Geognostica, pt. 1, pi. xliv, fig. 2. 



— Bigshy, 1878. Thesaurus Devonico-Carboniferus, p. 295. 



— Etheridge, 1888. Brit. Foss., pt. 1, Palaeozoic, p. 277. 

 Sanguinolites ([)ars), Etheridge, 1888. Ibid., p. 289. 



Allorisma (pars), Miller, 1889. N. Amer. Geol. and Palaeontol., p. 459. 

 Non — Worthen, 1890. Geol. Surv. Illinois, vol. viii, p. 132. 



— (par.s), Keyes, 1893. Rep. Geol. Surv. Ohio, vol. vii, p. 475. 



Non Allorisma, Beushausen, 1895. Abh. Kon. Preuss. Geol. Landesanstalt., n. F., 



Heft 17, p. 250. 



Generic Characters. — Shell transverse, oval, equi valve, very inequilateral. 

 Anterior border of valve continuous with the anterior edge of the umbo. Bluntly 

 rounded in front and behind, posterior end somewhat broader than anterior. No 

 oblique ridge. Lunule large, depressed; escutcheon large. Valves marked by a 

 broad but shallow sinus at the junction of the anterior and middle thirds. 



Interior. — Adductor muscle-scars shallow and inconspicuous. Pallial line 

 sinuated. Inner surface marked by concentric grooves and ribs. Hinge simple, 

 edentulous. 



Exterior. — Surface ornamented by simple concentric ribs and sulci, crossed 

 by radiating rows of small tubercles ; the dorsal slope almost smooth. 



Observations. — This genus has been much misunderstood, owing to its close 

 resemblance in external character to Edmondia on the one hand, and to Sanguino- 

 lites on the other ; from both of which it is at once separated by the possession of 

 a well-marked and deep pallial sinus, as pointed out by King. Unfortunately the 



54 



