N0.1299. CAMBRIAN BRA CHIOPODA—WALCOTT. 591 



The outer surface is marked by fine concentric strine and growth 

 lines, and the inner layers or lamellte by very fine radiating stride. 

 The minute foraminal aperture is on the back side of the apex, open- 

 ing- almost posteriorly in some examples. 



This is a small species averaging from 1.5 to 2.5 mm. in length. 

 It occurs in immense numbers in limestone lentiles of the Para- 

 doxides da»hl zone of Newfoundland. It is also very abundant at 

 Hastings Cov^e. 



Foriiiation and locality. — Middle Cambrian, paradoxides zone, 

 Chapel Arm, Trinity Bay; Manuels Brook, Avalon Peninsula, New- 

 foundland; Hastings Cove, Kennebecasis River, and Dr. G. F. Mat- 

 thew identified it at Porters Brook, St. Martins, St. John Count}-, New 

 Brunswick. 



ACROTRETA OPHIRENSIS, new species. 



General outline transversely broad oval, sometimes nearly circular, 

 with the posterior margin slighth^ indented midway on the pedicle 

 valve by incurving to the false pedicle furrow. The pedicle valve is 

 convex and moderately elevated, the highest point being in front of 

 the foraminal aperture at about one-third the diameter of the shell. 

 Foraminal aperture large for the size of the shell and opening either 

 directly or obliquely backward. One specimen shows a short, narrow 

 area, with a triangular false pedicle furrow crossing it; false area 

 scarcely defined b}- the cardinal slopes, which incurve very gently; 

 median furrow well defined, rather strong, and nearly flat on the bot- 

 tom, the margins being sharply outlined in many specimens. The 

 shell sometimes curves over the false area so that the depressed apex 

 extends slightly bej'ond the posterior margin, but usually it is directly 

 on the line of the posterior margin or a little in front of it. Longi- 

 tudinal diameter of average size pedicle valve 3 mm., with a length 

 of 2 mm. to 2.5 mm.; elevation 1.5 mm. A few shells have nearly 

 the same length and width. The convexity of the brachial valve 

 averages 0.75 nmi. The minute beak of the brachial valve curves 

 down to the posterior margin from the somewhat elevated posterior 

 third of the vahe. 



Surface marked by fine concentric strife and marked lines of growth 

 which occasionally form concentric ridges. The shell is built up of a 

 chin outer la3^er and numerous thin inner layers or lamelhe that are 

 oblique to the outer layer over the central and outer portions, the 

 obliquity increasing toward the outer anterior and lateral margins. 



The interior of the pedicle valve shows a rather strong apical cal- 

 losity that extends nearly to the posterior inner margin of the shell; 

 distinct but relatively small cardinal scars, and narrow main vascular 

 sinuses that may be traced nearly to the antero-lateral margins of the 

 valve; the outlines of the visceral cavit}^ are indicated on one well- 



