BILLINGSELLID^. 



749 



Genus BILLINGSELLA Hall and Clarke.'^ 



Billingsella Hall and Clarke, 1892, Eleventh Ann. Kept. State Geologist New York for 1891, p. 273. (Described.) 



Billingsella Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum for 1891, p. 589. (Copy of 

 preceding reference.) 



Kutorgina Hall and Clarke [not Walcott], 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 90-94. (Copies 

 Walcott's description, lS86b, pp. 101-102, and discusses genus, but description and discussion also include refer- 

 ence to specimens now referred to Billingsella, Protorthis, Micromitra, Micromitra (Paterina), and Micromitra 

 (Iphidella) .) 



Billingsella Hall and Clarke (in part), 1892, idem, pp. 230-231. (Described and discussed as a new genus. The 

 genus as described also included species now referred to Nisicsia.) 



Billingsella Hall and Clarke, Schuchert (in part), 1897, Bull. U. S. Geol. Survey No. 87, p. 158. (Characterized 

 and discussed. The genus Protorthis is placed as a synonym of Billingsella, and among the species referred to 

 the latter genus are species belonging with both Protorthis and Nisusia.) 



Billingsella Hall and Clarke, Walcott (in part), 1905, Proc. IT. S. Nat. Mus., vol. 28, pp. 227-229. (Described and 

 discussed essentially as below. Species that are now referred to Winianella were included in the genus.) 



Billingsella Hall and Clarke, Grabau and Shimer, 1907, North American Index Fossils, vol. 1, p. 210. (Described.) 



Billingsella Hall and Clarke, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 148. 

 (Classification of genus.) 



Shell subquadrate or subsemicircular in outline. Contour unequally biconvex or plano- 

 convex. Shell impunctate. Surface striate or plicate. Ventral valve with the greatest con- 

 vexity; cardinal area moderately high, slightly inclined outward; delthyrium covered by a 

 convex plate which in the type species B. coloradoensis has a minute perforation near the apex; 

 teeth well developed, with dental plates extending to the bottom of the umbonal cavity and 

 forming the sides of a small area opposite the delthyrium, where the pedicle muscle was probably 

 attached. In the dorsal valve the cardinal area is strongly inclined, but less than 90° to the 

 plane of the valve. The delthyrium is partly covered by a convex chilidium, or it may be 

 altogether absent. Cardinal process single. A rudimentary spondylium is indicated for B. 

 dice. Shell structure dense, minutely granular, with minute pores scattered through the 

 calcareous lamellse. 



Type. — Orihis coloradoensis Shumard. 



Observations. — Hall and Clarke [1892c, p. 230] founded the genus on "Orihis pepina" Hall, 

 which is a synonym of "Orthis coloradoensis" Shumard. The material from the limestones of 

 Texas in the United States National Museum shows the form of the teeth in the ventral valve, 

 also the deltidium and the minute perforation near its apex. Hall and Clarke [lS92c, p. 230] 

 state in their diagnosis that "in rare instances (it) may be minutely perforated at the apex," but 

 do not name the species in which the perforation occurs or where the specimens showing it are 

 to be found. All the species known to me are biconvex or plano-convex; none are concavo- 

 convex as defined by Hall and Clarke [lS92c, p. 230]. 



The genus is essentially orthoid, but it differs in the presence of the arched deltidium and 

 its general aspect from typical examples of the Orthidte, and its shell is of a dense, nonfibrous 

 structure. 



o The synonymy for this genus does not give a complete record of the various genera under which the species now included in BilJingsella were 

 formerly placed; it gives only those references in which the genus is discussed or described. To complete the record the following mere generic 

 references are listed : 



Orthis Barrande [1848, p. 203]. 



Orthis Shumard [1860, p. 627). 



Orthis Hall [1863, p. 134; 1867, p. 113]. 



Orthis Davidson [1868, p. 314; 1869, p. 230]. 



Orihis Linnarsson [1876, pp. 10, 12, and 13]. 



Orthis Barrande [1879b, PI. LXH, fig. 11]. 



Orthis Whitfield [1882, p. 170]. 



Orthis? (Orthisina?) Hall [1883, PI. XXXVII, figs. 



16-19]. 

 Orthis Kayser [1883, p. 35]. 

 Kutorgina Walcott [1884b, p. 18]. 

 Orthisina Whitfield [ 1884, p. 144]. 

 Orihis? Walcott [1886b, p. 119). 

 Orthisina Walcott [18S6b, p. 120). 



Orthis Walcott [1887, p. 190]. 

 Orthis Oehlert [1889, p. 1139). 

 Orthis? Walcott [1891a, p. 612]. 

 Orthisina Walcott [1891a, p. 613). 

 Clitambonites (Gonambonitcs) Matthew [1895b, 



p. 267]. 

 Orthis Wallerius [1895, p. 66). 

 Orthis Pompeckj [1896b, p. 513]. 

 Orthis (Billingsella) Sardeson [1896, p. 96]. 

 Clitambonites Schuchert [1897, p. 184). 

 Billingsella Walcott [1899, p. 450). . 

 Billingsella Matthew [1903, p. 148). 

 Orthis iPlectorthis) Walcott [1905a, p. 270). 

 Billingsella Walcott [1908d, pp. 101 and 102]. 



