NO. 1395. CAMBRIAN BRA CHIOPODA— WALCO TT. 285 



The ventral valve is somewhat more elevated than the dorsal. Hinge area trian- 

 gular, sloping backward to the umbo, and bearing fine striae parallel to the hinge 

 line. Umbo elevated above the hinge line to a height fully equal to one-third of the 

 length of the valve. Foramen [delthyrium] large, truncate-pyramidal in outline. 



Surface of the valves ornamented by about twenty rounded plicse, radiating [in 

 the ventral valve] from the edge of the hinge area, opposite the foramen [delthyrium] 

 and not from the beak alone; those on the middle fifth of each valve are crowded 

 together, those outside of these are more prominent, and are continuous from the 

 umbo; those toward the hinge line are faintly marked and widely separated. The 

 radiating plicae do not [or rarely] increase by bifurcation. Both valves bear numer- 

 ous concentric striae, and are also marked by a few distinct squamose lines of growth. 



The mold or cast of the interior of the valves of this species is nearly smooth 

 or is marked by faint radiating stria^; the margin of the mold, however, often 

 exhibits a crenulated appearance corresponding to the plicae of the outer surface. 

 There is a wide, smooth median depression at the top of the mold of the dorsal valve 

 near the umbo. 



Length of the valve in 0. qaacoeiisis, 5 mm. ; width, 8 mm. 



Observations. — Doctor Matthew very kindly sent me his types of this 

 species. A comparison of them with P. hilUngsi shows that the two 

 species are quite distinct, and P. quacoensis is unlike any other shell 

 referred to the genus. 



As far as seen the free spondyliumof the ventral valve is short; the 

 teeth are clearly shown in the cast. The pseudo-cruralium of the dor- 

 sal valve is much more clearly defined than in P. Mllingsi, the area is 

 higher, and traces of the adductor muscle scars are preserved. 



Formation and locality. — Middle Cambrian. Paradoxides zone, 

 division Ic, Portland and at Porter's Brook, St. Martins, New Bruns- 

 wick. 



PROTORTHIS SPENCEI, new species. 



This is a strongly marked species despite the fact that only a few 

 specimens have been found, and these are flattened in the shale. It is 

 distinguished by its rounded, subquadrate outlines and narrow, sharp 

 ribs with strong interspaces — six ribs in a distance of 5 mm. at the front 

 margin. The area of the ventral valve has a broad delthyrium with 

 a concave plate or free spondylium, covering the greater part of it. 

 The interior surface of the shell is finely punctate. A flattened ven- 

 tral valve has a length of 17 mm. ; width, 18 mm. 



This shell is associated with P. nautes. It diflers from it in its 

 larger size, sharper ribs, and broader interspaces between the ribs. 



The species is named for Mr. R. S. Spence, of Montpelier, Idaho, a 

 gentleman who made large collections from the Middle Cambrian shales 

 of Idaho. 



Formation and locality .—Ma&^q, Cambrian. Argillaceous shales, 

 Wasatch Range, near Montpelier, Idaho. Shaly limestones, 3 miles 

 east of Antelope Springs, House Range, Utah. 

 Proc. N. M. vol. xxviii— 04 19 



