394 CAMBRIAN BRACHIOPODA. 



shells as they occur flattened out in the argillaceous shales. Surface of the shell marked by 

 concentric lines and striae of growth, and fine, slightly undulating stride in the interspaces, and 

 fine radiating striae; the interior surface of the shell was strongly pitted or punctate, especially 

 in the posterior half (PI. XXII, figs. 2, 2a, 2i, and 2j). The shell was relatively thin, and 

 formed of a thin outer layer and one or more inner layers or lamellae. 



One of the larger ventral valves from Missouri has a length of 8.5 mm.; width, 7.5 mm., 

 as it occurs flattened in the shale; an associated dorsal valve has a length and width of 8 mm. 

 The average size of the specimens from Tennessee is about 7 mm. for the ventral valve; a few 

 shells from Georgia are unusually large; one dorsal valve (PI. XXII, fig. 21) has a length of 

 15 mm., width 12 mm., in the flattened shell. 



As shown in the cast the area of the ventral valve is rather long, and is divided midway 

 by a strong pedicle fuiTow and marked midway between the furrow and the cardinal margins 

 by a narrow flexure line. The strife of growth cross the area parallel with its base and extend 

 over the cast of the pedicle furrow; they are very fine and closely grouped together on the 

 flexure line and on the lateral slopes. The area of the dorsal valve is rather long and extended 

 well out onto the cardinal slopes ; it is marked in several specimens by unusually strong flexure 

 lines; the striae of growth cross it parallel to its base, curving sharply forward at the median 

 line. From the condition of the casts of the cardinal area it is evident that it formed in both 

 valves a thin shelf, the undercut extending backward far under the area much as in Lingulella 

 amfla (Owen) (PI. XXVIII), Lingulella acutangula (Eoemer) (PI. XVII), etc. 



Casts of the interior of the ventral valve (PL XXII, fig. 2b) show in the visceral cavity (v) 

 traces of the heart-shaped pit (x). There are no traces of a median septum in the ventral 

 valve, but it is shown in the casts of a dorsal valve as a very narrow, clearly defined short 

 depression, extending from a point in front of the anterior lateral muscle scars back between 

 the central muscle scars (PI. XXII, fig. 2g). 



Only the anterior lateral muscle scars are distinctly shown in the ventral valve. In one 

 specimen from Tennessee the trapezoidal area (c) is well preserved, but the central scars and 

 middle and outside laterals can not be differentiated (PI. XXII, fig. 2f). 



In the dorsal valve the central muscle scars (h), the anterior laterals (j), and the trans- 

 medians (i) are all discernible. The anterior laterals are small and situated near the center of 

 the shell, the centrals occurring some distance back and near the median septum, somewhat 

 as in Lingulella ampla (Owen) (PI. XXVIII). Portions of the markings left on the interior of 

 the shell by the vascular system are shown on a cast of the interior. The main or trunk 

 sinuses are best shown in the ventral valve in specimens represented in Plate XXII, figures 2, 

 2a, 2b, and for the dorsal valve in figure 2i. The parietal scar (ps) is distinctly shown in 

 front of the visceral area of the ventral valve (PI. XXII, figs. 2 and 2b) and the dorsal valve 

 (figs. 2g and 2h) ; in both valves it extends out to the main sinuses (PI. XXII, figs. 2 and 2h), 

 but it is not observed beyond them. 



Observations. — This fine species is well characterized by the strongly pitted inner surface 

 and the elongate visceral area of the dorsal valve. The specimens from the type locality at 

 Mine Lamotte are usually more or less broken and crushed, but a few in the United States 

 National Museum show the form and outline and, more rarely, traces of the interior visceral 

 and muscle scar markings. The material from Tennessee is much more abundant and some- 

 what better preserved; a marked variation is shown in the size and number of the interior 

 pits or punctae, and a considerable range in the outline of the valves; the latter is mainly to 

 be attributed to distortion as the result of compression and a slight movement in the shale. 

 Most of the specimens from Tennessee are about the same size as those from Missouri, but a 

 number of larger shells were found about 50 feet lower in the section which are nearly double 

 the average size of the specimens from Missouri and Tennessee. I am not able to discover 

 any other differences that lead to considering them as a distinct species. The specimens are 

 flattened in the shale, which gives rise to more or less distortion. The most nearly related 

 species is Oholus loillisi (Walcott) (PL XXIII) of the Middle Cambrian of Tennessee. The latter 

 differs in being shorter in proportion to its width, in the nearly transverse, obtuse posterior 



