OBOLIDiE. 509 



striae of growth cross the area and the pedicle furiow parallel to its base. The area of the 

 dorsal valve is partly shown in the figured specimen. It is rather long and marked by numerous 

 fine transverse stride. The only interior markings preserved are traces of the main vascular 

 sinus in the ventral valve and a portion of the narrow ridge on each side of the central groove 

 of the vascular cavity. 



Observations. — This is a large fine species that occurs in the siliceous slates at Point Levis. 

 It may be compared with the Lower Oi'dovician species, Ololus selwyni (Matthew) and Lingulella 

 (Lmgulepis) roherti (Matthew). 



Billings [1862b, p. 72] states that a single valve, found in the "Calciferous sandrock" 

 at the eastern end of the island of Montreal, is rather strongly convex, especially on the 

 umbonal. 



Formation and locality. — Lower Ordovician: (319a [Billings, 1862b, p. 72]) Levis shales, Point Levis, Quebec, 

 Canada . 



Lingulella iris (Billings). 



1/ 



Plate XXVII, figm-e 2. 



Idngula iris Billings, 186§, Geol. Survey Canada, Paleozoic Fossils, vol. 1, p. 301, fig. 290. (Described as a new species, 

 see below for copy. The specimen represented by fig. 290 is redrawn in this monograph, PI. XXVII, fig. 2.) 



The original description by Billings follows: 



Shell small, subovate; sides parallel, or nearly so, in the lower two-thirds gently convex or somewhat straight; in 

 the upper one-thu-d converging to the beak with a convex slope; beak narrowly rounded; anterior angles rounded; 

 anterior margin, with a portion in the middle, somewhat straight. The only specimen collected is gently convex, a 

 somewhat flat space along the middle, and a flat or gently convex slope on each side to the margin in the upper two- 

 thirds. Surface with obscure radiating and concentric strite. Length, 4J lines; width, SJ lines. 



The only specimen of this species in the collection of the Geological Survey of Canada is 

 the one described by Billings [lS65a, p. 301]. It is a dorsal valve with an outline somewhat like 

 that of Lingulella arguta (Walcott) [PI. XXIV, fig. 5a]. 



The character of the limestone matrix and the small fragments of trilobites embedded in 

 it indicate that the specimen was taken from one of the bowlders of Cambrian limestone embedded 

 in the Ordovician limestone No. 2 of the Point Levis section [Walcott, 1890a, p. 111]. 



Formation and locality. — Upper Cambrian: (3I9d [Billings, 1865a, p. 301]) Limestone bowlder in Lower Ordo- 

 vician conglomerate, Point Levis, Quebec, Canada. 



. ^ Lingulella isse (Walcott) . 



Text figures 43A-F, page 510, and Plate XXXIX, figures 4, 4a-b. 



Oboliis {Lingulella) isse Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 330. (Characterized as a new .species.) 



This shell is rather strong and made up of several thin layers or lamellae. Its outer sur- 

 face is marked by concentric lines of growth, sometimes grouped in more or less elevated bands, 

 and over all there is a thin encrusting or scabrous layer that has a minutely granular, dull 

 surface, somewhat like that of Lingulella (Lingulepis) gregwa (Matthew), but very much finer 

 in its granulations or points. The inner layers of the shell are dark, shiny, and marked by 

 concentric lines of growth and radiating striae. 



The longest ventral valve has a length of 16 mm. The proportions of length and breadth 

 of the valves are as follows : 



Dimensions, in millimeters, of valves of Lingulella isse (Walcott). 



Length. Width. 



[Elongate 16 9 



Ventral valves ^Medium 10 7 



[Short and broad 11 9 



I Elongate 6.5 4.5 



Medium 5 4.5 



Medium 11 8.5 



Short and broad 10.5 9 



