388 CAMBRIAN BRACHIOPODA. 



that Barrande's figure [1879, PI. CLII, fig. ii: 4] shows in the arrangement of the internal char- 

 acters a remarkable similarity to the large valve of Schmidtia. (This figure is represented in 

 PI. XII, fig. 3, of this memoir.) A comparison with O.feistrrianteli (Barrande) (PL XII, fig. Id) 

 shows the relation of the interior markings in the two species. However, the figure of 0. corn- 

 plexus, which is an internal cast, has a pointed projection that indicates the presence of the 

 transmedian and anterior lateral muscle scars much closer to the margm of the shell than the 

 other species of the genus. I think, however, that we are justified in referring the species pro- 

 visionally to Obolus. The specimens figured by Barrande [lS79b, PI. XCV, figs, ii: 1-2] do not 

 appear to me to represent this species. The valve from Kruschna Hora (PI. XII, fig. 3a) 

 probably represents a dorsal valve. All the characters known to me are shown by the figures. 

 Hall and Clarke [1892c, p. 73] considered that the species might be a genuine Obolella. 



Formation and locality. — Lower Ordovioian: (303i) Mage dl, Kruschna Hora; (303h) Etage dl, at Milinsky 

 Wrch, near Woleschna; and (303g) Etage dl, at Babenberg; all [Barrande, 1879b, Pis. XCV and CXI] in Bohemia, . 

 Austria-Hungary. 



Obolus cyane (Billings). 



Plate XXVII, figures 4, 4a-b. 



Lingula cyane Billings, 1865, Gaol. Survey Canada, Paleozoic Fossils, vol. 1, p. 216, figs. 200a-d, p. 215. (Described. 



Billings's type specimens are redrawn in this monograph, PL XXVII, figs. 4, 4a-b, but it is impossible further 



to identify his figures -with those in this monograph.) 

 Glossina cyane (Billings), Schucheet, 1897, Bull. U. S. Geol. Survey No. 87, p. 224. (Merely changes generic 



reference.) 



General form ovate cuneate, broadly rounded at the front and sides, with the ventral 

 valve subacuminate and the dorsal valve broadly rounded at the beak; valves rather strongly 

 convex, especially the dorsal. Surface marked by concentric strise and slight undulations of 

 growth and by very fine radiating striae; when the outer surface is exfoliated the inner layers 

 or lamellae are marked by numerous radiating striae and concentric lines and undulations of 

 growth ; the casts of the interior show essentially the same markings as the inner layers, except 

 over the visceral area, which is largely covered with fine papillaj corresponding to the minutely 

 pitted surface of the shell's interior. The shell is thick and built up of a thin outer layer and 

 numerous inner layers or lamellfe arranged over the anterior portions of the shell obliquely to 

 the outer surface. Three ventral valves have an average length of 7 mm., with a width of 

 6 mm. ; a dorsal valve 6 mm. in length is the same in width. The area of the ventral valve, 

 as shown in a cast, is divided at the center by a strong pedicle furrow and about halfway 

 between the pedicle furrow and the lateral margin by a sharp flexure line. The striae of 

 growth cross the area parallel with its base and show very clearly on the cast of the pedicle 

 furrow. The area forms a thin shelf between tlie pedicle groove and the lateral margins, the 

 undercut extending well back under the area. Tlie area of the dorsal valve is relatively short 

 and narrow, scarcely showing when viewed from above. 



The cast of the visceral cavity is strongly marked, but in none of the specimens are the 

 muscle scars shown. The central groove is shown in the cast by a rounded ridge, and the path 

 of advance of the trapezoidal area (c), in wliich the central, middle, and outside lateral muscle 

 scars occur, is beautifully shown by Plate XXXII, figure 4, the transverse ridges representing 

 the lines of growth. The main vascular sinuses are fairly well shown in the same figure. There 

 are no traces of a median septum in the ventral valve, but this structure is clearty shoAva in 

 the casts of the dorsal valve, extending forward between the anterior lateral muscle scars. 



The cast of the interior of the dorsal valve shows that in the adult the shell was thickened 

 over the visceral area and that the muscle scars were located on a comparatively elevated plat- 

 form. The position and form of the anterior lateral and central muscle scars and the direction 

 of the scar of tlie parietal band are fairly well shown by Plate XXVII, figure 4b, as is also the 

 umbonal scar (g). 



Observations. — This is a most interesting species on account of its preserving well into 

 Ordovician time the characteristics of well-marked forms of Lingulella from the Middle and Upper 



