714 CAMBRIAN BRACHIOPODA— WALCOTT. 



The form can not well be identified with the closely related /. labradorica 

 or its variety SH-antonensis, or /. stissiiigeufiis, on account of these pecul- 

 iar surface characters, and the name I. alabamae)isi.s is ])roposed for it. 



In general form of the valves this species is the same as /. labradorica 

 and I.stis,si)u/(')isi.s. The sj)eciti(; <litTcrence from them, as far as known, 

 is in the surface character. The convexity of the valves is unknown, 

 owin<;- to the con)pression of the sliells in the shale, and we have no 

 information of the area or the i)seudodeltl(lium. It may be that with 

 the obtaining of better material, especially from the limestone, this 

 species will be referred to as a variety of I. stissingensis. Shell sub- 

 stance corneous. 



Formation and localiti/. — Middle Cambrian, Coosa Valley shale. Cowan 

 Creek section, Cherokee County, Alabama; also in Rogers ville shale, 

 4 miles northeast of Rogeriiville, Tennessee, back of Big Creek, south- 

 east of Harlans Knob. (No. 2G432, U.S.N.M.) 



YORKIA, new genus. 



Shell inarticulate, subcircular to suborbicular in outline. Apex 

 of ventral (pedicle) valve perforate, marginal, with a false area and a 

 pseudodeltidium. The cast of the interior of the valve shows a fora- 

 men which penetrated obli(]uely upward and backward through the 

 thick umbonal portion of the shell. Two narrow furrows converge 

 from the side of the foraminal opening toward the longitudinal mesial 

 depression and then diverge toward the anterolateral portions of the 

 shell. 



The dorsal (brachial) valve has a well-defined area and an obscure 

 pseudodeltidium. The interior of this valve has a pair of broad, diverg- 

 ing, shear-shaped furrows passing directly forward from the beak for 

 a short distance and then div^erging to the outer margin, but not suf- 

 ficiently to affect the outward curve of the inner margin. 



Shell substance probably calcareous. External surface marked with 

 more or less i^rominent concentric stria^ and lines of growth. 



Ti/pe. — 1 o rli-ia ican ncr i . 



The area and ])seudodeltidium of the ventral valve resemble the 

 same parts in 'fremafobolxs insignis, Matthew,' but the foramen is 

 quite different, and generally the interior of the dorsal valve also serves 

 to distinguish the forms. To J)iscinop.sis, Matthew,- there is a resem- 

 blance in the markings of the interior of the dorsal valve. Discinopsis, 

 however, is founded upon a small, apparently corneous shell, which 

 so far as known, has no area or pseudodeltidium, and it is closely 

 related to Acrothele. Yorkia differs from Acrothelc in its pronounced 

 area, substance of shell, and ])lace of origin of vascular trunks. I do 

 not know of any other genus of the tiiphonotretida' with which it can 

 be compared. 



' Can. Rec. oi Sci., V, 18i)8, p. 277. 

 n^al.N. Y., VIII, Pt. 1, 181t2, p. 105. 



