432 CAMBRIAN BRACHIOPODA. 



The muscle scars are not so well shown in this species as in the associated Oholus (Ling'u- 

 lobolus) spissus. In the ventral valve the anterior lateral and transmedian scars are so closely 

 united with each other that they can not be differentiated. It is the same with the centrals, 

 wliich appear to be crowded in with the middle and outside laterals. In the dorsal valve the 

 central and anterior lateral muscle scars are clearly defined, and the position of the trans- 

 median and the outside and middle laterals is fairly well shown in one specimen. The marldngs 

 left on the shell by the vascular system are confined to the main or trunk sinuses, which are 

 imperfectly represented. 



Observations. — Bilhngs [1872b, fig. 4] illustrated an elongate form of the ventral valve, 

 and Matthew [lS95b, PI. I] a shorter ventral valve, and with it, as the dorsal valve, the dorsal 

 valve of 0. (i.) spissus. The form that Matthew [1895b, p. 262] has described as the variety 

 cuneata is probably a dorsal valve of 0. (i.) affinis. 



This is one of the largest shells that has been referred either to Oholus or its subgenera. In 

 form it resembles other cuneate species, but it differs from all ia the thickness of the shell and 

 the slight definition of the cardinal areas of the valves. It is quite probable that if we had a 

 series representmg the stages of growth the young shells would be referred to Lingulella, as 

 Linguloholus to me appears to be an extravagant development of a species of Lingulella that 

 has had unusually favorable conditions for growth. Oholus {Linguloholus) ajfinis is associated 

 with 0. (L.) spissus (Billings) and Oholus (Westonia) rogersi (Walcott). 



Formation and locality. — lower Ordovician: (114b)« Sandstone 1 mile {1.6 km.) north of Lance Cove, Great 

 Belle Island, Conception Bay, Newfoundland. 



(326a [Grabau, 1900, p. 613]) Limestone pebbles in a Carboniferous conglomerate north of Fall River, Bristol 

 County, Massachusetts. 



Obolus (Lingtjlobolus) spissus (Billings). 

 I 



Plate XVI, figures 2, 2a-k; Plate XLII, figures 3, 3a. 



Lingulella ? spissa Billings, 1872, Canadian Naturalist, 2d ser., vol. 6, no. 4, pp. 468-469, figs. 5a-c, p. 467. (Described.) 

 Lingulella f spissa Billings, 1874, Geol. Survey Canada, Paleozoic Fossils, vol. 2, pt. 1, pp. 67-68, figs. 36a-c, p. 66. 



(Described. Figs. 36a-c are copied from figs. 5a-c, respectively, of the preceding reference.) 

 Lingulella? spissa Billings, 1882, Geol. Survey Newfoundland, Kept. Progress for 1881, Appendix, p. 15, PL III, 



figs. 12a-c. (Text and figures copied from preceding reference.) 

 Sphxroholus spissus (Billings), Matthew, 1895, Trans. Roy. Soc. Canada, 2d ser., vol. 1, pp. 263-266, PL I, figs. 5a-c. 



(Original description [Billings, 1872b, pp. 468-469] copied and species described and discussed.) 

 Oholus {Linguloholus) spissus (Billings), Walcott, 1898, Am. Jour. Sci., 4th ser., vol. 6, p. 327. (New locality 



mentioned.) 

 Sphxroholus spissus (Billings), Grabau, 1900, Occas. Papers Boston Soc. Nat. Hist., No. 4, vol. 1, pt. 3, pp. 622-623. 



(Described.) 



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

 obtusety rounded; valves strongly convex, the dorsal being about one-third more so than the 

 ventral. The proportions of the convexity are sho%vn by the outlines accompanying the figures. 

 The surface of the shell is marked by concentric Imes of growth and very fine undulating, sub- 

 imbricated, concentric strife and very fine radiating strife, which, crossing the fine concentric 

 strise, cut the surface up into minute squares or parallelograms. This type of surface orna- 

 mentation also occurs on one or two of the inner layers of the shell just beneath the outer layer. 

 The surface of the inner layers, especially that of the lamellae forming the anterior lateral thick- 

 enings of the shell, is marked by numerous flattened strise and over the central portions by 

 raised, threadlike strife; the interior of the shell and some of the interior layers are marked 

 by fine pits or punctse, arranged in more or less concentric lines. In addition, there is a finely 

 punctate surface that can be seen only with the aid of a high magnifying power. 



The shell is formed of a thin outer layer and numerous inner layers or lamella, the latter, 

 as oblique lamellas, becoming more numerous over the anterior and lateral portions of the 



a 114b is the type locality, though the specimens in the United States National Museum to which that numher is assigned were collected 

 much later than the type specimens. 



