NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA GRANT 57 



flattened anterior surface nearly perpendicular to dorsal and ventral 

 surfaces. Internal features, the spondylium and camarophorium, are 

 typical for Devonian species in the Stenoscismatacea. The camaro- 

 phorium is shallow, and only gently curved longitudinally. 



ATRIBONIUM PINGUE Grant n. sp. 



Plate 2, figs. 1-lc ; figure 10 



Shell large for genus, strongly biconvex ; outline subtrigonal to sub- 

 pentagonal, widest slightly anterior to midlength ; profile wedge-shaped 

 but curved, becoming very thick at anterior of adults ; commissure uni- 

 plicate; fold high, flat crested, normally beginning more than 5 mm. 

 anterior to brachial beak, producing rather high elevation of valve ; 

 sulcus broad, shallow, also beginning more than 5 mm. anterior to 

 beak ; costae distinct, rounded, simple, beginning 5-8 mm. anterior to 

 beaks, numbering four or five on fold, one fewer in sulcus, normally 

 three on each flank; anterior margin convex in outline, convex but 

 somewhat flatter in profile ; growth lines fine, closely spaced ; growth 

 laminae stronger, irregularly spaced. 



Pedicle valve moderately strongly convex, with greatest swelling 

 anterior to beak, slight prominence of anterolateral margins, elevating 

 costa on each side of sulcus of some specimens ; geniculation at anterior 

 sharp in few specimens, gentler in most ; beak short, suberect ; beak 

 ridges sharp, short ; delthyrium constricted by pair of conjunct deltidial 

 plates ; foramen slotlike, not observed to pierce apex of beak. 



Brachial valve more strongly convex, especially so transversely ; 

 beak somewhat attenuate, apex hidden beneath deltidial plates ; anterior 

 geniculation of valve normally rather gentle. 



Pedicle valve interior with spondylium sessile for about 1 mm. in 

 apex of beak, elevated anteriorly on low median septum, extending 

 forward one-third to one-half length of valve. 



Brachial valve interior with camarophorium extending anteriorly 

 about the same proportionate distance. 



Holotype.—USNM 141919, plate 2, fig. lc. 



Growth. — The pattern of growth of this species seems typical for 

 the genus. Points representing the length-width ratio cluster narrowly 

 along a straight line, whereas those representing the length-thickness 

 ratio spread more widely along a curve of gentle acceleration (fig. 10) . 

 This latter curve could be projected toward the length-axis and inter- 

 sect it just above zero with little change in curvature. The line of 

 length-width however, must bend somewhat to flatten its curvature in 

 order to intersect the length-axis in the same region, indicating some 

 allometry in increase in width at early shell stages. Small juveniles 

 probably were elongate and very thin. 



