552 CAMBRIAN BEACHIOPODA. 



Lingulepis starri var. Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, pp. 193-197, PI. 



XIV, figs. 2a-c. (Gives an essential copy (rearranged) of the description given by Walcott, 1901, pp. 692-694, 



and describes and discusses the specimens referred by Walcott to Obolus (Lingulepis) gregwa as belonging to 



an undetermined variety of Matthew's "Lingulepis starri.") 

 Lingulepis starri exigua Matthew, 1903, idem, pp. 197-198, PI. XIV, figs. 3a-d. (Described and discussed as a new 



variety.) 



General form elongate ovate ■\vith the ventral valve acuminate and the dorsal valve ovate 

 triangular in outKne. The outline of the valves varies, as shown by the series of figures on 

 Plate XLIII and by many other specimens not illustrated. The convexity of the valves A^aries 

 with the condition of the preservation, those from the sandstone being rather strongly convex, 

 while those in the shale are very much compressed. On the dorsal valve of the youngest 

 shells there is a marked and rather broad, shallow sinus extending from the umbo to the front 

 where it flattens out. 



One of the largest ventral valves has a length of 21 mm., with a width of 18 mm. A 

 dorsal valve 16 mm. in width has the same length; other examples are a little wider than long. 



Surface of the shell marked by concentric striae and undulations of growth, over which 

 there is a series of very fine, elevated, sharply undulating and inosculating lines that form a 

 minute irregular network over the surface, very much Hke that of Lingulella (Lingulepis) 

 gregwa (Matthew), except that the irregular lines are very much finer on the latter. Where 

 the lines are strongly elevated the effect is that of a minutely granulose surface. In some 

 examples the surface suggests an incrusting or scabrous outer layer of shell covered Vfith 

 minute points. When the thin outer layer of the shell is exfoliated the surface of the various 

 bright, sliiny, inner layers is minutely granulose, in addition to the flattened, radiating strise 

 and concentric lines of growth. The interior surface of both valves is often marked by con- 

 centric rows of strong pits or punctte very much as in Lingulella davisi (McCoy) (PI. XXXI, 

 fig. 6g). In some specimens the lines of punctse extend over the surface of the visceral cavity 

 so as to obscure the vascular markings and muscle scars. In some examples only a few scat- 

 tered punctse occur, while in others they are present over nearly the entire surface. The small 

 shells are tliin, but the larger ones are built up of a very tlun outer layer and several inner 

 layers or lamellae that are more or less obUque to the outer surface, especially over the anterior 

 and lateral portions of the shell. 



The plane of the cardinal area of the ventral valve is nearly coincident, near its edges, with 

 the edge of the shell. The area is long and extends well forward on the cardinal slope. It is 

 divided midway by a narrow, rounded, deep pedicle furrow, and about half way between the 

 pedicle furrow and the lateral margins by an unusually well-defined flexure line wliich is in 

 fine with the main vascular furrows of the interior of the valves; fine strife of growth cross the 

 area and arch around the pedicle furrow parallel to the base of the area. There is practically 

 no undercut beneath the area except near the flexure fine at the frontal margin of the area. 

 The area of the dorsal valve is short, narrow, and crossed by fuie lines of growth parallel to 

 its base. 



The cast of the visceral cavity in the ventral valve shows it to have been relatively smaU 

 and usually confined to the posterior half of the shell, although in some shells it extends past 

 the center (PL XLIII, fig. Iq). There are no traces of a median septum in the ventral valve; in 

 the dorsal valve, at the bottom of the groove between the central muscle scars, there is a sUghtly 

 elevated median line that extends forward to the anterior margin of the visceral cavity beyond 

 the anterior lateral muscle scars. The visceral cavity of the dorsal valve usually extends 

 forward to about the center of the valve, but in a series of specimens collected in 1903 a number 

 of interior casts show the front of the visceral area varying in position from back of the center 

 to nearly the frontal margin of the sheU ; it varies in width and outline very much as the shells 

 vary, being wide in broad shells and narrow in elongate forms. 



The markings left on the shell by the vascular system are very strong and beautifully pre- 

 served in some portions. The direction and size of the main sinuses are v.^ell shown by the 

 illustrations; in some shells there is a double groove with a slight ridge between; in others the 



