OBOLID^. 393 



to be an exceedingly fine papillose surface, which is apparently produced by the inosculation 

 of- irregular, raised strise, as on the surface of Oholus (Westonia) ella (Hall and Wliitfield) and 

 Lingulella ferruginea Salter and on a larger scale by Lingulella radula Matthew. Wlien the 

 outer layer of the shell is exfoliated, very fine concentric and radiating strise occur on the surface 

 of the inner layers. The shell is thin and formed of an outer layer and one or more thin layers 

 or lamellae. 



The average length of the ventral valve is about 5 nun.; width, 4 mm. The dorsal valve 

 is a little shorter. 



The rather long area of the ventral valve is divided midway by a strong pedicle groove 

 (PL XXIII, fig. 5). The area of the dorsal valve is clearly defined on casts of the interior; it 

 is about three-fifths the width of the valve and is arched forward at the center. 



The casts of the interior of the valves show traces of the vascular markings, but nothing 

 very definite can be said of them. 



Ohservations. — This pretty little species is closely related to Lingulella ferruginea Salter, 

 with which it is associated in the shales of Manuels Brook. It is distinguished from the latter 

 by its broad form and thinner shell. 



Formation and locality. — Middle Cambrian: (la) Shales near the top of No. 6 of the Manuels Brook section; 

 (1) shales of zone A of No. 7 of the Manuels Brooi section; and (2) shales of zone B of No. 7 of the Manuels Brook sec- 

 tion; all on Manuels Brook (see Walcott, 1891b, p. 261, for position in section). Conception Bay, Newfoundland. 



Obolus? inflatus Westergard. 



Obolus f inflatus WestekgIrd, 1909, Medd. irkn Lunds Geol. Paltklubb, Ser. B, No. 4 (Aftryck ur K. Fysiografiska 

 Sallskapets Handl., N. F., Bd. 20), p. 76, PL V, fig. 25. (Described in Swedish as a new species; see below 

 for translation.) 



The original description by Westergard follows: 

 Interior of shell unknown, hence the generic identification is uncertain. The outer contour is almost elliptical, 

 being somewhat less broad than high. The thin shiny shell is posteriorly sharply convex and slopes from there to the 

 anterior margin. It has somewhat uneven, fine, but very distinct concentric striae and indistinct radial strise. Even 

 where the shell is exfoliated the radial striation is apparent. 



Formation and locality. — ^Passage beds between the Upper Cambrian and the Ordovician: (310x [Westergard, 

 1909, p. 76]) The uppermost limestone stratum, in beds equivalent to the Ceratopygeliinestoae, at Jerrestad, Province 

 of Malmohus, Sweden. 



, Obolus ismene Walcott. 



Plate XI, figures 3, 3a-b. 



Obolus ismene Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 325. (Characterized as below as a new species.) 



This species is characterized by its elevated umbo, flattened posterior lateral margins, and 

 relatively thin shell. 



All that is known of the exterior surface indicates that it was nearly smooth, marked only 

 by fine concentric strise of growth. The inner layers of the shell are beautifully marked by 

 fine concentric and radiating strise that give the surface a cancellated appearance. The shell 

 is built up of several layers or lamellae that become more oblique to the outer surface toward 

 the front. 



Formation and locality. — Upper Cambrian: (369) Sandstone in the Elvins formation, in the eastern limits of 

 the town of Flat River, St. Francois County, Missouri. 



Obolus lamborni (Meek). 

 Plate XXII, figures 2, 2a-n. 



Lingulella ? lamborni Meek, 1871, Proc. Acad. Nat. Sci. Philadelphia for 1871, vol. 23, pp. 185-187, fig. 1. (Described 

 and discussed as a new species.) 



Lingulella lamborni Meek, Keyes, 1894, Missouri Geol. Survey, vol. 5, pt. 2, pp. 38-39, PL XXXV, figs. 5a-d. (De- 

 scribed.) 



General form broadly ovate, with the ventral valve obtusely acuminate and the dorsal 

 valve rather broadly oval; convexity apparently moderate, judging from specimens of the 



