OBOLID^. 403 



all other species of the genus known to me. Seven specimens were collected from a shaly compact 



limestone, all as casts. Remnants of the corneous shell are 



preserved, which show it to have been very thin, and the 



interior casts show that it did not retain any impressions 



of the animal sufSciently strong to be impressed on the cast- 



A short, rather narrow cardinal area occurs on both the 



ventral and dorsal valves. Outer surface smooth, with a 



few lines of growth. The largest ventral valve has a length -A. 



of 17 mm. and a width of 22 mm. A less distorted dorsal "iguee 36.-ow«. memmnaceus j^icm a, 



_ Cast of ventral valve (U. S. Nat. Mus. Cat. No. 



valve has the same length and width, 15 mm. sscwa). B,castofdorsaivaive(u. s. Nat. mus. 



The specific name was given because of the very thin C'''- no. 5.%74b). Both natural size. 



.. , in "^^^ specimens represented are from Locality 35ff, 



almost membranaceous shell. Eldon limestone on Mount Bosworth, British Co- 



T-, ».,...«,. /«,. N .1 . > innf Inmbia. Figure 36A is copied from Walcott 11908d, 



Formation and locality. -Middle Cambrian (35g) : About 4,100feet pi yn, fig. ii|; it represents the type specimeu. 

 (1,250 m.) above the Lower Cambrian and 860 feet (262 m.) below the 



Upper Cambrian in the shaly limestones in No. 2 of the Eldon limestone, at the north end of the amphitheater north- 

 west of the main ridge of Mount Bosworth, north of the Canadian Pacific Railway between Hector and Stephen, on 

 the Continental Divide, between British Columbia and Alberta, Canada. 



ObOLUS ? MENEGHINII Walcott. 

 Plate XXX, figures 17, 17a. 



Not Lingula petalon (Hicks MS.) Davidson, 1868, Geol. Mag. vol. 5, p. 308, PL XV, fig. 16. (Not taken up in this 



monograph.) 

 Not Lingula petalon Davidson, 1871, British Fossil Brachiopoda, vol. 3, pt. 7, No. 4, p. 337, PL XLIX, fig. 30. (Not 



taken up in this monograph.) 

 Lingula petalon Bornemann [not Davidson], 1891, Nova Acta Acad. Cses. Leop. -Carol. Germanicse Naturae Curiosorum, 



Bd. 56, No. 3, p. 438, PL XIX (XXXIV), figs. 12-14. (Described in German; see below for translation. Fig. 



14a is copied in this monograph, PL XXX, fig. 17.) 

 Obolella sp. (?) Bornemann, 1891, idem, p. 440, PL XIX (XXXIV), fig. 18. (Characterized in German. Fig. 18 is 



copied in this monograph, PL XXX, fig. 17a.) 

 Obolus (?) meneghini Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 684. (Bornemann's description, 1891, p. 438, 



translated, and species discussed as below as a new species.) 



Bornemann says [1891, p. 438]: 



Rounded triangular, frontal margin at times almost straight. Shells rather flat, their arching being greatest in 

 the middle. Concentric and rather coarse lines of growth. Size, 5-11 mm. 



The specimen referred to "Obolella sp. (?)" by Bornemann [1891, p. 440] is from the slate 

 of Porto Canal Grande. It is not an Obolella and may be identical with the species from the 

 sandstones. 



The shells referred to "Lingula petalon" [Bornemann, 1891, p. 438] suggest Obolus in form 

 and surface ornamentation and are tentatively referred to that genus and a specific name 

 given them in recognition of the work of Prof. Giuseppe Meneghini. 



Formation and locality. — Middle Cambrian: (354c) Yellow, friable sandstone at Punta Pintau (Canal Grande); 

 (354d) yellow friable sandstone at Gruguetta; and (354e) slate at Porto Canal Grande; all [Bornemann, 1891, pp. 438 

 and 440] in the island of Sardinia, Italy. 



Obolus mickwitzi Walcott. 



Plate X, figures 1, la-k. 



Obolus mickwitzi Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 386-387. (Described and discussed as below as 

 a new species.) 



General form rounded ovate, with the ventral valve broadly subacuminate, and the dorsal 

 valve obtusely rounded; valves, as shown by the casts, moderately convex, which would give 

 a rather strongly convex shell, as fragments show that it was quite thick over the central 

 portions. Fragments of the shell showing the outer surface indicate that it was marked by 

 concentric lines and striae of growth ; radiating striae may have been present ; they are strongly 

 developed when the outer surface is exfoliated. The casts of a number of examples of the 



