OBOLIDiE. 513 



Not Obolus (Palxobolus) Zcws Matthew, 1903, Geol. Survey Canada, Kept. Cambrian Rocks Cape Breton, pp. 144-146, 

 PL X, figs. la-f. (Referred in this monograpli to Obolus (Palxobolus) bretonensis lens.) 



General form broadly ovate. The ventral valve is subacuminate and the dorsal valve very 

 broadly ovate to subsemicircular. The convexity of the valves is moderate, the ventral valve 

 being most prominent along the center, with the posterolateral slopes somewhat flattened 

 toward the margin. 



Surface of the shell marked by fine, concentric strise and lines of growth, and the inner 

 surface by concentric lines and very fine radiating striae. The shell is thinner than most species 

 of the genus, resembhng in this respect Oholus f murrayi Billings, Lingulella Ixvis Matthew, 

 and L. hella (Walcott). It is formed of several layers or lamellae that are slightly obhque to 

 the outer layer. Matthew [1901, p. 274] speaks of minute pits on the outer surface. These 

 also appear on the inner layers. I have been unable to determine whether the tliin calcareous 

 crust mentioned by Matthew [190,1a, p. 274] is really the true outer layer or simply a thin calca- 

 reous deposit. 



The largest specimen of a dorsal valve in the collection has a length of 15 mm., with a 

 width of 13 mm. The corresponding ventral valve was probably 1 or 2 milhmeters longer. 



Observations. — In the material collected by Loper in 1901 there are some specimens that 

 show the form of the ventral and dorsal valve of tliis species. The shell is broader and rounder 

 than I supposed when studying the material Matthew sent me. It is quite distinct from Lin- 

 gulella hella (Walcott) and L. concinna Matthew, ^^ath which I placed it. The interior markings 

 are those of Lingulella, but it may be that more perfect material would prove it to belong to 

 one of the subgenera of Obolus. 



Matthew [1903, p. 201] refers to this form as a variety of Lingulella Isevis. With the mate- 

 rial from Cape Breton and Newfoundland for comparison, I am not sufficiently sure to follow 

 him in this, as it appears to be specifically cdstinct from Isevis. 



Further remarks on tliis species occur under Lingulella concinna (p. 487). 



Formation and locality. — Upper Cambrian: (10r)'» Thin calcareous layers in the arenaceous shales of Division 

 C3a? of Matthew at McAdam shore. East Bay, east of Bras d'Or Lake, eastern Cape Breton, Nova Scotia. 



Lingulella leos (Walcott). 



Plate XXIV, iigures 2, 2a-c. 



Obolus (Lingulella) leos Walcott, 1888, Proc. U. S. Nat. Mus., vol. 21, p. 407^08. (Described and discussed essen- 

 tially as below as a new species.) 



Shell small; general form elongate ovate \vith tlae ventral valve subacuminate. The 

 valves are rather strongly convex in the narrow form of the species. Average length of a 

 ventral valve is 5 mm. ; the largest ventral valve has a length of 6 mm. ; the dorsal valve is 

 somewhat shorter. The width of the valve varies considerably in shells occun-ing in the 

 same hand specimens in the limestone. This is shown by Plate XXIV, figures 2 and 2a, for the 

 ventral valve, and 2b and 2c for the dorsal valve. The surface of the shell is marked by fine con- 

 centric lines and striae of growth, and very fine, interrupted, radiating striae ; casts of the inte- 

 rior of the shell show stronger radiating striae than the outer surface; also in many specimens 

 unusually large papillae that fill the pits or punctas of the inner surface. The number and 

 strength of the papillae vary in different casts. The shell appears to have been rather tliin, 

 and formed of a thin outer layer and one or more thin inner layers or lamellae. 



Casts of the interior of the ventral valve show a well-defined area, divided midway by 

 the cast of a strong pedicle groove. The area of the dorsal valve is obscured by adhering 

 fragments. On casts of the ventral valve traces of the visceral cavity (v) and the main vascular 

 sinuses (vs) occur, and in the dorsal a narrow, long median sinus is clearly defined; also the 

 casts of the central and anterior lateral muscle scars (PI. XXIV, figs. 2b and 2c). 



olOr is the type locality, though the specimens in the United States National Museum collections to which that number is assigned were 

 collected later than the type specimens. 



62667°— VOL 51, pt 1—12 33 



