-NO. 1395. CAMBRIAN BRA CHIOPODA— WALCOTT. 309 



from the umbo and two near the sides that may have sometliing- to do 

 with the muscle scars or vascular sinuses. 1 thought so in ISSG," but 

 am not sufficiently confident of it now to state it as a settled conclu- 

 sion. Fine punct* occur on the inner layer of the shell; also numer- 

 ous radiating lines about one-half a millimeter apart. 



Dorsal valve gently convex in young shells. With increase in size 

 the umbo becomes more elevated and the apex })oints upward or termi- 

 nates at the union of the pseudo area and the upward slope of the shell 

 on the umbo. In some shells there is a tendency for the valve to 

 become slightly concave in the space between the margins and the 

 elevated umbo. The pseudo area of the valve is narrow and with little 

 character; on some shells it slopes beneath the apex, and on others it 

 slopes backw^ard, forming a low angle with the surface oi the valve. 

 The interior of the dorsal valve shows a median septum, with two 

 central scars, and the anterior lateral scars. Numerous small vascular 

 canals radiate from central concave area toward the tiattened anterior 

 and lateral half of the valve. A cast of the interior shows two vascular 

 canals radiating forward from near the apex. Radiating lines occur 

 on the interior of the same character as those of the ventral valve. 



Ohservations. — Since writing on this species in 188(3 I have collected 

 ■ipecimens showing the character of the pseudo areas of the valves, and 

 also obtained further information relative to the interior of the dorsal 

 valve. The rudimentary or pseudo areas are less advanced in develop- 

 ment than those of Iphidella^ and the muscle scars of the dorsal valve 

 are much like those of OholeUa and Oholns. 



The specimens from Bic Harbor and east of Swanton, Vermont, are 

 better than those from the type locality at L'Anse au Loup. Many of 

 the V^ermont shells are larger and more fully developed, l)ut specimens 

 of the same size as those from L'Anse au Loup and Bic Harbor are 

 identical in the characters available for comparison. 



Formation and locality. — Lower Cambrian. L'Anse au Loup lime- 

 stone with OlenelluH thoiupsonlvit L'Anse au Loup, on the north shore 

 of the straits of Belle Isle, Labrador. In bowlders of limestone con- 

 taining fragments of Olenellus, in Cambrian conglomerate, at East 

 Point, Bic Harbor, Province of Quebec, Canada. The species is 

 abundant in lenticular masses of limestone intercalated in argillaceous 

 and arenaceous shales carrying OleneUuH tliom,j>soni on the Bullard 

 farm, about two miles east of Swan ton, Vermont. 



Dr. Eduard von ToU^^ identities and illustrates as Kntorgina cin- 

 (juhda Billings a dorsal valve that occurs with other forms that may be 

 referred to the Lower Cambrian fauna of the Cambrian of Siberia. 



Locality. — Near the Tschurskaja Station, on the Lena. 



«Bull. U. S. Geol. Survey, No. 30, p. 103. 



^Beitrage zu Kenntniss des Sibiriseheii Cambrium, I. M^m. de I'Acad. Imp. dea 

 Sci. de St. Petersbourg, VIII ser., 1899, pp. 26-27. 



