OBOLID^. 405 



rather strong concentric lines of growth and numerous very fine concentric stride. The inner 

 layers of shell are shiny black and ornamented with numerous fine, radiating striae and concentric 

 lines. Shell built up of several thin layers or lamellse that form a thin shell over the umbonal 

 region that gradually thickens as the short, oblique lamellfe become more numerous toward the 

 front and side margins. The three specimens in the collection average 3 mm. in transverse 

 diameter; the ventral is a little longer than the dorsal valve. 



A partly exfoliated ventral valve shows a well-marked visceral area, extending forward 

 about one-third of the length of the shell; also narrow main vascular sinuses starting near the 

 apex and extending obliquely forward well into the valve, about midway between the median 

 line of the valve and the lateral margins. This neat little shell is distinguished by its nearly 

 circular outline, low convexity, and small size. 



Formation and locality. — Middle Cambrian : (CI) Lower shale member of the Kiulung group [Blackwelder, 

 1907a, pp. 37 and 40 (part of the 3d list of fossils), and fig. 10 (bed 4), p. 38], 2 miles (3.2 km.) south of Yenchuano- 

 Sintai district, Shantung, China. 



Obolus? mixor Barrande. 



Plate XV, figure 6 



Obolus 1 minor Barrande, 1868, Faune silurienne des environs de Hof, en Bavifere, p. 105, fig. 68. (Described in 



French as a new species. Fig. 68 is copied in this monograph, PI. XV, fig. 6.) 

 Obolus ? minor Barrande, 1868, Neues Jahrb. fur Mineralogie for 1868, p. 693, unnumbered plate, fig. 69. (Text 



and figure copied from preceding reference.) 



Of this species the author [1868a, p. 105] remarks: 



We know only the impression figured. It differs from 0.? palliatus Barrande by having a well-marked beak and 

 in being rather more elongate. The surface is ornamented by rather close concentric striae regularly spaced. Length 



7 mm., width 7 mm. 



It is not improbable that this represents the ventral valve of OJ palliatus, but in the absence 

 of specimens for comparison it is left with the designation given by Barrande. 



Formation and locality. — Passage beds between the Upper Cambrian and the Ordovician: (303c [Barrande, 

 1868a, p. 105]) suburbs of Hof, Bavaria, Germany. 



^ Obolus? mirandus (Barrande). 

 Plate XII, figures 4, 4a. 



Lingula? miranda Barrande, 1879, Systgme silurien du centre de la Boheme, vol. 5, PI. CXI, figs, i: 1-3. (No text 

 reference. Figs. 3A and la are copied in this monograph, PI. XII, figs. 4 and 4a, respectively.) 



In form this species is much like that of Ololus ancilhis (Barrande) (PI. XII). The traces 

 shown of the interior markings by figure 4a are similar to those of Ololus feistmanteli (Barrande) 

 (PI. XII, fig. 1). The outer surface, as shown on the figure, recalls that of 0. (Westonia) clla 

 (Hall and Whitfield) (PI. XLVII). With only the two illustrations given by Barrande, it 

 is impossible more than provisionally to refer the species to Oholus. 



Formation and locality.— Lower Ordovician: (303k [Barrande, 1879b, pi. CXI]) Etage dl at Hradischt, Bohe- 

 mia, Austria-Hungary. 



Obolus ? murrayi Billings. 



Plate XV, figure 12. 



Obolus ? murrayiBiLLiNGS, 1865, Geol. Survey Canada, Paleozoic Fossils, vol. 1, p. 362. (Described as a new species; 

 see below for copy. The type specimen upon which Billings based his description, but which he did not 

 figure, is represented in this monograph, PI. XV, fig. 12.) 



The original description by Billings follows : 



The specimen is very nearly circular, broad ovate, width a little greater than the length, uniformly and mod- 

 erately convex; the shell black and corneous and covered with fine concentric striae. Length, 7 lines; width, about 



8 lines. Of this species only a single valve was found. * * * It belongs probably to the Quebec group. 



This appears to be a true Oholus, as far as can be determined from the exterior surface 

 of a single specimen. Its large size and strong concentric strife indicate that Billings's refer- 

 ence to the "Quebec group" (Lower Ordovician) is probably correct. 



