■OBOLID^. 463 



of a marked mesial depi-ession on the dorsal valve. The shell is rather thin and made up of 

 several very thin layers or lamellse. The outer surface is marked by fine radiating strise, con- 

 centric strife and lines of growth, and fine, more or less undulating, transverse lines that cross 

 both the radiating and concentric lines. The transverse lines appear to be the edges of slightly 

 elevated imbricating lamella of the shell. 



Formation and locality. — Lower Ordovician : (201a) Pogonip limestone, east slope of the ridge east of Ham- 

 burg Ridge, Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



Tipper Cambrian: (64) Limestone near the Bullwhacker mine, Eureka district [Hague, 1892, Atlas], Eurelca 

 County, Nevada. 



(S4j) About 700 feet (213.4 m.) above the Middle Cambrian and 525 feet (160 m.) below the top of the Upper Cam- 

 brian, in the arenaceous limestone forming 2c of the St. Charles formation [Walcott, 1908f, p. 192], in Blacksmith Fork 

 Canyon, about 10 miles (16.1 km.) east of Hyrum, Cache County, Utah. 



Obolus? (Westonia?) lamellosus (Barrande). 



Plate XII, figures 7, 7a-d. 



Lingula lamellosa Barrande, 1879, Systeme silurien du centre de la BohSme, vol. 5, PL CVI, figs, i: 1-5; PL CXI, 

 figs, ix: 1-3. (Not described, but figured as a new species. PI. CVI, figs, i: 2A, i: 3f, and PL CXI, figs, ix: 

 2A; IX : lA, and ix: If are copied in this monograph, PL XII, figs. 7, 7a-d, respectively.) 



Obolus {Westonia?) lamellosus (Barrande), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 691. (Merely changes 

 generic reference.) 



This species appears to be the Bohemian Lower Ordovician representative of Obolus ( Wes- 

 tonia) stoneanus (Wliitfield) of the Upper Mississippi Valley Middle Cambrian fauna. The 

 two forms agree in relative size and proportions and in type of surface ornamentation. This may 

 be seen by comparing figures 2, 2a-g, Plate XXVIII, with figures 7, 7a-d, Plate XII. Another 

 point of similarity is that both species are very abundant in the localities in which they occur. 



The principal differences to be noted are that OJ ( WJ) lamellosus has apparently a thicker 

 and stronger shell than 0. (W.) stoneanus. This, however, may be due to the fact that all the 

 specimens of the latter species are more or less flattened in the shaly sandstone, and that the 

 shell substance has been largely removed by solution. It is on account of the resemblance of 

 the two forms that Barrande's sjiecies is referred to the genus Obolus and subgenus Westonia, 

 despite the absence of any knowledge of the area or the interior vascular markings or muscle 

 scars. 



It is hoped that the paleontologists of Bohemia will take up the study of this species and 

 others that have been referred to Obolus, in order to establish clearly their generic relations. 



Formation and locality. — Lower Ordovician: (3031 [Barrande 1879b, PL CVI]) Etage dl, Libetschov, 

 Bohemia, Austria-Hungary. 



Obolus (Westoxia) notchensis Walcott. 



1/ Plate LXIII, figure 9. 



Obolus (Westonia) notchensis Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No, 3, p. 69, PL VII. fig. 13. (Discussed 

 as below as a new species. Fig. 13 is copied in this monograph, Plate LXIII, fig. 9.) 



This species is represented by two specimens of the ventral valve that have the general 

 outline of Lingulella ampla (Owen) (PI. XXVIII, figs, la and If). The exterior surface is 

 marked by concentric lines of growth and transverse, irregular, imbricating lines mucli like 

 those of Obolus {Westonia) stoneanus (A^liitfield) (PL XXVIII, fig. 2) and 0. (TF.) ipUs (PI. 

 XLIX, figs. 4a-c). The form of the valve differs fi'om that of the latter species. 



The largest specimen has a length of 11 mm., with a maximum width of 9 mm. 



The specific name is derived from Notch Peak, Utah, on which the species occurs. 



Formation and locality. — Lower Ordovician: (105t) Thin-bedded, bluish-gray limestone [Walcott, 1908f, 

 p. 173 and Pis. XIII and XIV], at the summit of Notch Peak, House Range, Millard County, Utah. 



Obolus (Westonia) eogersi (Walcott). 



'-"' Plate XLII, figures 2, 2a-d. 



Lingula prima Rogers [not Conrad MS., Hall], 1861, Proc. Boston See. Nat. Hist., vol. 7, p. 390. (Mentioned.) 

 Lingula antiqua Rogers [not Emmons], 1861, idem, p. 390. (Mentioned.) 



