80 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



radial plication or ornamentation absent. Valve edges butting except at 

 posterolateral slopes, there brachial valve edge slightly overlapping 

 narrow flange on pedicle valve ; concentric growth lines weak, closely 

 spaced, some forming low laminae at wide intervals. 



Pedicle valve slightly swollen in umbonal region, strongly convex 

 longitudinally through sulcus, flanks relatively flat ; beak slightly at- 

 tenuate, suberect to erect, pressed against brachial umbo in some speci- 

 mens ; beak ridges short, gently rounded ; delthyrium small, triangular, 

 sides constricted by small, triangular, disjunct deltidial plates ; foramen 

 small, elongate, normally open but filled by brachial beak in some 

 specimens. 



Brachial valve strongly convex transversely, flatly convex along 

 crest of fold ; beak blunt, apex within pedicle valve. 



Pedicle valve interior with large dental plates converging toward 

 floor, meeting to form scoop-shaped spondylium, normally sessile near 

 beak, elevated on short septum duplex toward anterior, extending for- 

 ward about one-third length of valve. 



Brachial valve interior with short, undivided hinge plate giving rise 

 to pair of long, slender, ventrally curved crura ; median septum begin- 

 ning at beak, extending forward about 1 mm. along floor, anterior edge 

 curved forward thus extending length of septum above floor ; top of 

 septum expanded on each side to form camarophorium, originating on 

 floor of valve in extreme apex, rising high above floor toward anterior, 

 extending forward slightly farther than spondylium, not connected to 

 hinge plate, intercamarophorial plate absent. 



Holotype.— Cooper, 1956a, p. 524, plate 61, figs. 20-25, USNM 

 124412a ; this paper, plate 9, fig. 1. 



A B C D E F G 



Fig. IS. — Psilocamara renfroarum Cooper, Capps Limestone Member of 

 Mineral Wells Formation, Tex., transverse sections of 3 specimens. 



A. Section near beak, Xca.4.5, USNM 124412g; Cooper, 1956a, Text-fig. IB, 

 No. 4 : intercamarophorial plate absent. 



B-E. Transverse sections X?4ca.4, one specimen from Cooper, 1956a, Text-fig. 

 1, part B : B. 0.3 mm. from beak, Cooper's fig. 7. C. 0.65 mm. from beak, 

 Cooper's fig. 9. D. 0.77 mm. from beak, Cooper's fig. 10, intercamarophorial 

 plate clearly absent. E. 1.0 mm., Cooper's fig. 11. F. 1.2 mm., Cooper's fig. 13. 



G. Section X5, about 1.00 mm. from beak, USNM 142047, intercamarophorial 

 plate absent. 



