OBOLID^. 381 



partial cast in the limestone. The shell is relatively thin and formed of a very thin outer layer 

 and one or more thin inner layers or lamellse, which thicken the shell from the umbonal 

 region and toward the front and sides. 



A cast of the interior of a dorsal valve that is referred to this species shows that a strong 

 median ridge was present; also a median septum and a strong main vascular sinus. The area is 

 short and marked by rather prominent flexure lines, as indicated by the flexures in the transverse 

 lines of growth. 



Ohservations. — This species might be taken for the young of 0. matinalis (Hall) or 0. msera 

 (Hall and Wliitfield), were it not for the great difl'erence in the thickness of the shell. It occurs 

 at a slightly higher horizon at the base of the Pogonip limestone. 



Formation and locality. — Lower Ordovician (63) Limestone at the base of the Pogonip limestone northeast of 

 Adams Hill, Eureka district [Hague, 1S9-2, Atlas], Eureka County, Nevada. 



Tipper Cambrian: (61) Limestone in the Dunderberg shale [Walcott, 1908f, p. 184], a little south of the Hamburg 

 mine, Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



Oboltjs? ancillus (Barrande). 



Plate XII, figure 2. 



Lingula ancilla Barrande, 1879, Systlme silurien du centre de la Boh6me, vol. 5, pt. 1, PL CXI, fig. vi: 3. (No 

 text reference. Fig. 3 is copied in this monograph, PL XII, fig. 2.) 



This is a small shell of which we have only the one figure given by Barrande [1879b, PI. CXI, 

 fig. VI : 3] from which to express an opinion as to its generic relations. The configuration of the 

 valve and the lamellose character of.the shefl, as indicated by the portions adhering to the cast, 

 are what has led me to make the provisional reference to Oiolus. There are no interior characters 

 shown in the figure. 



Formation and locality. — lower Ordovician: (303g [Barrande, 1879b, PL CXI]) Etage dl, at Rabenberg, 

 Bohemia, Austria-Hungary. 



r Obolus apollinis Eichwald. 

 Text figures 4 and 15, page 299; Plate VII, figures 1-8, 10-17; Plate XIV, figures 6, 6a. 



Obolus apollinis Eichwald, 1829, Zoologia specialis, vol. 1, p. 274, PL IV, figs. 5a-b. (Described in Latin as a new 



species.) 

 Ungula plana Pander, 1830, Beitrage zur Geognosie des russischen Reiches, pp. 59 and 163, PL XXVIII, figs. 3a-b, 



5a-b. (Characterized in German on p. 59; description of plate on p. 163.) 

 Ungula plana or convexa Pander, 1830, idem, p. 163, PL XXVIII, figs. 2a-b. (Only the description of the plate 



occurs on p. 163.) 

 Ungula rotunda Pander, 1830, idem, pp. 59 and 163, PL XXVIII, figs. 4a-b. (Characterized in German on p. 59; 



description of plate on p. 163.) 

 Ungula ovata Pander, 1830, idem, pp. 59 and 154, PL III, fig. 23 (not PL XXVIII, figs. 6a-b, referred to Obolus 



(Schmidtia) celatus). (Characterized in German on p. 59; description of plate on p. 154.) 

 Ungula transversa Pander (in part), 1830, idem, pp. 59 and 163, PL XXVIII, figs. 7a-b, 8a-b? (not PL III, fig. 24, 



which represents a specimen of Obolus apollinis quenstedti). (Characterized in German on p. 59; description of 



plate on p. 163.) 

 Ungula triangularis Pander, 1830, idem, pp. 59, 154, and 163, PL III, fig. 25, PL XXVIII, figs. 9a-b. (Characterized 



in German on p. 59; descriptions of plates on pp. 154 and 163.) 

 Obolus apollinis Eichwald, 1840, Jom'. Natur- und Heilkunde Medizinischen Akad. St. Petersburg, pts. 1 and 2, p. 167. 



(Not seen.) 

 Orthis singula von Buch, 1841, Archiv fiir Mineralogie, Bd. 15, Hft. 1, pp. 7-8, PL II, fig. 9. (Described and discussed 



in German, as belonging with the " Unguliten.") 

 Obolus apollinis Eichwald, 1843, Beitrage zur Kenntniss des russischen Reiches, Bd. 8, No. 2, p. 140. (Discussed in 



German.) 

 Obolus apollinis Eichwald, de Vernbuil (in part), 1845, Geologic de la Russie d' Europe, by Murchison, de Verneuil, 



and de Keyserling, vol. 2, pt. 3, pp. 290-292, PL XIX, figs. 3a-d. (Described and discussed in French; see Mat- 

 thew, 1892, pp. 43^4, for translation. De Verneuil includes Obolus apollinis ingricus, Obolus (Acritis) anti- 



quissimus, and Obolus {Mickwitzella) siluricus in this species.) 

 Obolus apollinis Eichwald, Kutorga, 1848, Verhandl. Russ.-kais. min. Gesell. St. Petersburg for 1847, No. 12, pp. 251 



and 252. (Discussed in German.) 

 Aulonotreta polita Kutorga (in part), 1848, idem, pp. 279-282, PL VII, figs. lOa-f. (Described and discussed in 



German as a new species. The text includes Obolus apollinis, Obolus apollinis ingricus, and Oboius {Mickwitz- 

 ella) siluricus.) 



