600 CAMBRIAN BRACHIOPODA. 



^ Obolella (Gltptias) favosa (Linnarsson). 

 Plate LV, figures 2, 2a-d. 



Lingula (?) favosa Linnarsson, 1869, Ofversigt af K. svensk. Vet.-Akad. Forhandl. for 1863, vol. 26, No. 3, pp. 



356-357. (Described and discussed in Swedish as a new species.) 

 Lingula (?) favosa Linnarsson, 1869, Geol. Mag., vol. 6, p. 406. (Translation of the preceding reference.) 

 f Disdnaf sp. Kjbrulf, 1873, Om Skuringsmarker, Glacialformationen, Terrasser, og Strandlinier, etc., 2:Sparagmit- 



fjeldet, p. 83, figs. 12 and 13. (No text reference.) 

 Obolella {Glyptias) favosa (Linnarsson), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, pp. 675-676. (Described and 



discussed essentially as below.) 



General form ovate, with the ventral valve subacuminate and the dorsal valve obtusely 

 rounded; valves moderately convex. The dorsal valve is abruptly curved downward at the 

 beak to the plane of the edge of the shell, while the beak of the ventral valve is slightly above 

 the margin, the posterior edges of the shell curving up to meet it. Surface of the shell marked 

 by very fine concentric lines or strise of growth, crossed transversely by undulating, slightly 

 lamellose lines in almost identically the same manner as in Obolus ( Westonia) stoneanus (Wliit- 

 field) of the Upper Cambrian of Wisconsin (PI. XXVIII, fig. 2d). When the outer surface 

 of the shell is exfoliated or worn off by attrition, which is the usual condition, the surface 

 of the inner layers shows fine radiating and concentric striae. The shell is formed of a very 

 thin, highly ornamented outer layer and numerous inner layers or lamellae ; the latter over the 

 anterior portions are oblique to the outer layer, and when the shell is partly exfoliated they 

 appear as imbricating layers very much as in Obolus matinalis (Hall). 



The largest ventral valve in the collection has a length of 7 mm. and a width of 6 mm. 

 An associated dorsal valve 6 mm. long has a width of 6.25 mm. 



The area of the ventral valve is narrow and rises slightly to meet the beak, which is ele- 

 vated above the posterior margin. The pedicle tube or foramen is short and small, and, judging 

 from the appearance of the specimens where the beak of the valve is broken away, it opened 

 near the apex of the beak. On the dorsal valve there is no evidence of a true area except in 

 the presence of a narrow, thickened rim somewhat like that of the dorsal valve of Bicia gemma 

 (Billings). None of the muscle scars are shown in the ventral valve. The position of the 

 central and anterior lateral scars of the dorsal valve is indicated near the outline of the vis- 

 ceral cavity (PL LV, fig. 2c). Of the vascular markings, the main sinuses are clearly shown 

 in each valve, also the outline of the parietal scar. All that is known of them is well shown on 

 Plate LV. 



Ohservations. — This beautiful little shell has remained without illustration since Linnarsson 

 [1869a, p. 356] gave it a name, based on the "singular sculpture" of the outer shell. In a 

 collection made for me by Mr. Schmalensee, a collector in the Geological Survey of Sweden, 

 there were several specimens showing casts of the interior more or less imperfectly. From 

 these I was able to ascertain that the shell has the generic characters of Obolella, although 

 differing from the typical species of that genus in the character of the surface ornamentation. 

 The outer surface has been seen only on the posterior umbonal portion of the valves in the 

 shells collected. 



Kjerulf [1873, p. 83, figs. 12 and 13] illustrates, without text reference, a form that appears 

 to be referable to this species. It occurs in Locality 324 at Tomten, Norway, in association 

 with Obolella mobergi, Holmia Jcjerulfi, and Arionellus. 



Formation and locality. — lower Cambrian: (309c) o "Fucoid sandstone" at Billingen, east of Skara; and (309d) 

 "fucoid sandstone" at Lugnds, 8 miles [12.8 km.) south-southeast of Mariestad; both [Linnarsson, 1869a, p. 357] in the 

 Province of Skaraborg, Sweden. 



(324 [Kjerulf, 1873, pp. 73 and 83]) Green shales with interbedded calcareous sandstone at Tomten, in Ringsaker, 

 near Lake Mjosen, Province of Hedemarken, Norway. 



a Specimens from this locality are included in the collections of the United States National Museum. 



