444 GEOLOGY OF THE YELLOWSTONE NATIONAL PAKK. 



In a review of the Cambrian Brachiopoda, now being prepared, the 

 Cambrian species referred to the subgenus Lingulepis will be fully illus- 

 trated. 



Obolus (Lingulepis) acuminatus var. meeki Walcott. 



PI. LX, figs. 1, la. 

 Lingulepis meeki Walcott, 1897: Am. Jour. Sci., 4th series, Vol. Ill, p. 405. 



Shell small, attenuate, marked by rather strong concentric lines and 

 strise of growth, and by interrupted irregular radiating stria?. 



Ventral valve narrow, elongate; beak acuminate, rostral slopes long, 

 nearly straight, passing gradually into the curvature of the anterolateral 

 margins, and posteriorly meeting at a very acute angle; front strongly 

 rounded. Lenth of valve, 8 mm.; width, 3.5 mm., the widest portion being 

 near the anterior extremity. Beak slightly upcurved, the longitudinal 

 median line straight, or even slightly concave from the apex of the beak to 

 the middle, where it begins to slope gently to the frontal margin; trans- 

 verse curvature very slight anteriorly, more convex near the beak. 



Dorsal valve more convex than the ventral, linguliform; beak depressed, 

 bluntly rounded, curving evenly and gradually to the semitruncate anterior 

 margin. 



The interior markings of this shell have not been ascertained, but the 

 external characters are such as to make a reference to the genus Lingulepis 

 more than probably correct. The flat acute-acuminate ventral valve, with 

 its elevated or retrorse beak, which is not covered by the smaller dorsal 

 shell, is peculiarly characteristic of Lingulepis. 



There is a form from Texas, probably identical with Obolus (Lingulelht) 

 perattenuatus, that might be mistaken for this species, but it is an undoubted 

 Lingulella, and does not show the external characteristics of Lingulepis. A 

 comparison with the young and narrow specimens of 0. (L.) acuminatus 

 shows it to be clearly distinct from that species; the posterior rostral slopes 

 of 0. (L.) acuminatus possess a peculiar incurving which is not shown in 

 the variety meeki. 



Formation and locality: Middle Cambrian, upper beds of Flathead 

 terrane, Crowfoot section, Gallatin Range, Yellowstone National Park. 



