OBOLIDiE. 501 



The original description by Matthew is as follows: 



A narrowly ovate species, somewhat straight on the sides, and broadly rounded in front. 



The ventral valve has an obtusely pointed beak, bent down at the apex. Sides of the valve somewhat sharply 

 sloped in the posterior half and gently eloped in front. Interior. — This shows an area nearly half a millimeter long, 

 and a visceral callus extending about half the length of the valve. The lateral ridges within the valve extend as far; 

 and in fi'ont of them, reaching to within a sixth of the length of the valve from the front, is a pair of arched vascular 

 grooves not far from the margin of the valve; numerous external branches from these trunk grooves extend to the 

 flattened margin of the valve. The individual length of these branches is about equal to the width of the main 

 gi'oove. 



The dorsal valve is obtusely rounded at the hinge area, which is very short, and here and at the sides the valve 

 is strongly arched downward, but is gently sloped down in front. Interior. — In front of the linear cardinal area is a 

 pair of pits marking the insertion of the cardinal muscles. The middle of the valve for more than half the valve's 

 length has a flattened band marking the progress of the central muscles during the growth of the shell. At the front 

 this band is about one-sixth or one-eighth of the width of the valve, and at its sides are faint prints of the central 

 muscles; and at the ft-ont are two pairs of minute pits, one or both of which marks the position of the anterior laterals. 

 The place of the posterior laterals is marked by a series of small pits near the .margins in the posterior third of the valve. 

 In fi-ont of these pits are the strong arched grooves left by the vascular trunks, which extend across the middle half 

 of the valve near its margins. 



No examples have been obtained showing the surface markings, except those near the front of the valve; but 

 both valves show fi-om four to six ridges of gi-owth in the anterior quarter of the valve. These ridges are broadly 

 curved in the middle part, but more abruptly at the sides. 



Ventral valve 4 mm. long and 2.5 mm. wide. The dorsal valve is nearly one-half millimeter shorter than the 

 ventral. 



This species is of nearly the same size as L. insulse, but is less elliptical in outline, and the valves are more flat- 

 tened in front; the area of the ventral valve also is longer, and that of the dorsal shorter than in that species; also the 

 central group of muscles is not set so far forward as in that of the dorsal of the species cited. 



This species differs fi'om L. atavus of the Etcheminian teiTane in having the central muscles of both valves set 

 farther back. 



The exact horizon of this species is uncertain, as the outcrop is in an isolated basin [Mat- 

 thew, 1903, p. 51]. Matthew correlated it with his section on the lithologie character of the 

 matrix. The form is very much like that of Lingulella collicia (Matthew), and it appears to 

 be identical with small shells of the latter species. 



Formation and locality. — Middle Cambrian: (325a [Matthew, 1903, p. 190]) Shales of Division C2c of Mat- 

 thew's [1903, p. 49] Bretonian on the eastern slope of the valley of McNeil Brook, on the road to Trout Brook, in the 

 Mira River valley, eastern Cape Breton, Nova Scotia. 



Lingulella franklinensis (Walcott). 



Plate XXVI, figures 3, 3a-b. 



Obelus (Lingulella) franklinensis Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 404-405. (Described and dis- 

 cussed essentially as below as a new species.) 



Shell small, ovate, moderately convex, with the apex of the dorsal valve subacuminate. 

 Surface of the shell marked by rather strong lines and striae of growth, with very fine, slightly 

 irregular, wavy strise between the coarser concentric striae. Two ventral valves referred to 

 this species have a length of 3 and 3.5 mm., respectively, with a width of about 2.75 mm. 

 There are no dorsal valves in the collection. A partial cast of the interior of the shell carries 

 an impression of radiating strise, a strong cast of a narrow pedicle furrow, and a few concentric 

 hnes of growth. If the shell represented by Plate XXVI, figure 3b, belongs to this species, 

 the interior surface was also marked by scattered bits of punctse. 



Ohservations. — This species is founded on three specimens of the ventral valve that occur 

 in the hmestones interbedded in dark shales above the Lower Cambrian Olenellus-hesiT'mg 

 shales. A larger shell (PI. XXVI, fig. 3b) has the same surface characters and occurs at the 

 same relative geological horizon, and it may belong to this species; the only specimen of it 

 in the collection is apparently a dorsal valve. The exact stratigraphic horizon has not been 

 determined, but from the associated species of Agnostus and PtycJioparia it appears that the 

 reference should be to the Middle Cambrian. 



