DESCRIPTIONS OF SPECIES. 441 



posterioi' truncation. The maximum transverse diameter is only about 15 mm., and 

 the shell resembles the type referred by Meek to Schizodus rossicus de Vern. ? " more 

 pei'haps than any other. Schizodim symmetricus Calvin* is another similar though 

 larger species, and Sch. affinis Herrick'^ is also closely related. 



Locality and harizon. — San Juan i-egion (station 2205); upper part of Hermosa 

 formation. 



NUCULA Lamarck, 1801. 



NUCULA VEXTRICOSA Hall ? 



1858. Nucula ventricosa. Hall, Geol. Surv. Iowa, vol. 1, pt. 2, p. 716, pi. 24, figs. 4, 5a, b. 



Coal Measures. 

 1872. Nucula ventricosa. Meek, U. S. Geol. Surv. Nebraska, p. 204, pi. 10, figs. 17a-c. 



Upper Coal Measures: Nebraska City and Rock Bluff, Nebr. 



Lower Coal ^Measures: AVest Virginia. 



Coal Meaures: Illinois. 

 1882. Nucula veiitricosii. White, Geol. Surv. Indiana, 11th Kept., p. 371, pi. 42, figs. 9, 10. 



Coal Measures: Sullivan County, Ind. 

 1884. Nucula ventricosa. AVhite, Geol. Surv. Indiana, 13th Kept., p. 146, pi. 27, figs. 9, 10. 



Coal Measures: Sullivan County, Ind. 

 1888. Nueida ventricosa. Keyes, A.cad. Nat. Sci. Philadelphia, Proc, p. 233. 



Lower Coal Measures: Des Moines, Iowa. 



1895. Nucula ventncosa. Keyes, Missouri Geol. Surv., vol. 5, p. 121, pi. 45, figs. 3a, b. (Date of 



imprint, 1894.) 

 Lower Coal Measures: Clinton, Mo. 

 Upper Coal Measures: Kansas City and Gentry, Mo. 



1896. Nucula ventricosa. Smith, Leland Stanford Junior Univ. Publ. ; Cont. Biol. Hopkins Seaside Lab., 



No. 9, p. 35. 



Lower Coal Measures: Conway County, Ark. 

 1896. Nucula ventricosa. Smith, Am. Phil. Soc, Proc, vol. 35, p. 245. 



Lower Coal Measures: Conway County, Ark. 

 1900. Nucula ventricosa. Beede, Univ. Geol. Surv. Kansas, Kept., vol. 6, p. 150, pi. 22, figs. 9, 9b. 



Upper Coal Measures: Kansas City, Rosedale, Turner, Topeka, Grand Summit. 



Indeterminable generically but probably a Nucula^ Schizodus, or an Edinondia., 

 this is the only material at pre.sent in the collection upon which the identification of 

 Nucula ventricosa in the lists of the Leadville monograph ''- could have been based. 



Locality and horizon. — Leadville district (station 2255); Weber formation (?). 



aGeol. Surv. Illinois, Kept., vol. 5, 1873, pi. 26, figs. 17a-e, 18. 

 6 State Univ. Iowa Lab. Nat. Hist., Bull., vol. 1, p. 176, pi. 2, figs. 3a, b. 

 oSci. Lab. Denison Univ., Bull., vol. 2, 1887, p. 41, pi. 4, figs. 22, 22a. 

 liU. S. Geol. Surv., Men., vol. 12, 1886, p. 70. 



