592 CAMBEIAN BEACHIOPODA. 



The position of the depressions (a) these ridges filled on the area is shown by figures Ih, li; 

 they are triangular areas on each side of a raised, central, triangular space that corresponds 

 in position to the pedicle furrow in species like Lingulella (Lingulepis) acuminata (Conrad) 

 (PL XLII, fig. 2a). In Obolus apollinis this portion of the area is sometimes slightly elevated, 

 with a depressed furrow on either side (PI. VII, figs. 6, 7). The cast of the cylindroconical 

 pedicle tube or foramen has been observed in a cast of the interior of the ventral valve (fig. le). 

 This is best seen in Oholella atlantica (PI. LV, figs. If, Ig, Ih). The external foraminal opening 

 has not been observed. 



The muscle scars are unfortunately not well preserved. The general position of the trans- 

 median and anterior laterals is shown in the ventral and dorsal valves (i, j, PI. LV, figs. If, Ig) ; 

 the centrals (h) and the anterior laterals (j) in tlie dorsal valve (fig. Ih). The position of the 

 central, middle, and outside lateral muscle scars is indicated in the ventral valve by the outline 

 of the visceral cavity (v) as shown on figures le. If, but no individual scars can be determined. 

 The outside and middle laterals of the dorsal valve are merged with the transmedian in all 

 the specimens showing them at all; this is undoubtedly owing to the poor preservation of the 

 specimens. 



The main trunks of the vascular sinuses are fairly well shown in both valves; also the 

 outline of the parietal scar between the sinuses. A rather strong median ridge occurs in the 

 posterior half of the dorsal valve on which the small anterior lateral muscle scars are situated 

 (PI. LIV, figs. Ig-i). 



Observations. — When the validity of the genus Oholella was attacked [Hall, 1867, p. 110] 

 BiUings restudied this, the type species, and gave [1876, p. 176] an elaborate description of all 

 the characters he could determine. Through the kindness of the director of the Geological 

 Survey of Canada and of Prof. J. F. Whiteaves, I have had the opportunity of studying the 

 material in the Canadian Survey collection. Prof. Alpheus Hyatt also sent me specimens he 

 collected at L'Anse au Loup and I found some very good specimens in a small collection in 

 the United States National Museum, that were not accessible when I illustrated the species 

 in 1886 [1886b, PI. XI, figs. 1, la-b] and 1891 [lS91a, PI. LXXI, figs. 2, 2a-b]. Among the 

 new characters discovered are: (a) the narrow pseudo-pedicle groove; (b) the cast of the 

 cylindroconical pedicle tube or foramen; (c) the character of the area of the ventral valve; 

 (d) the vascular impressions of the interior of the ventral valve; these taken in connection 

 with the features shown by 0. atlantica Walcott establishes the genus Oholella as distinct from 

 Oholus and Dicellomus. 



The species 0. cTiromatica Billings is about the same size as 0. atlantica, but it differs in 

 outline, convexity, and details of the areas of both valves. I know of no other species with 

 which it is necessary to compare its specific characters. It is in association with Olenellus 

 tJiompsoni and other fossils characteristic of the upper portion of the Lower Cambrian fauna 

 in the Gulf of St. Lawrence and the Lake Champlain region. The bits of limestone brought 

 from Labrador show great numbers of the separated valves, indicating that they occur in 

 large numbers in one or more layers. 



Von Toll [1899, p. 27, PL I, fig. 27] illustrates a specimen from 3 miles (4.8 km.) beyond 

 Bestjachskaja station, on Lena River, Siberia, which he compares with Oholella cTiromatica 

 BiUings. It is too imperfect to determine with any degree of certainty what it may be. 



Formation and locality. — Lower Cambrian: (392a) Limestones at L'Anse au Loup, on the north shore of the 

 Straits of Belleisle; (392c [Billings, 1872a, p. 218]) at the Straits of Belleisle; and (3921) arenaceous limestone at 

 Point Amour, Straits of Belleisle; all in Labrador. 



(314f) Limestone of B7 of the section at Bonne Bay [Walcott, 1891b, p. 255], Newfoundland. 



(338p) Sandy limestone one-fourth mile (0.4 km.) northwest of schoolhouse No. 7 in Greenwich, Cambridge 

 quadrangle (U. S. Geol. Survey), Washington County, New York. 



^^ Obolella ckassa (Hall). 



Text figure 14, page 299; Plate LIV, figures 2, 2a-n. 



Orbicular crassa Hall, 1847, Nat. Hist. New York, Paleontology, vol. 1, p. 290, PL LXXIX, fig. Sa. (Described.) 

 Avicula f desquamata Hall, 1847, idem, p. 292, PL LXXX, figs. 3a and 3b. (Described.) 



