OBOLID^. 517 



LiNGULELLA MANTICXJLA (White). 

 Plate XX, figures 1, la-c. 



Lingula? manticula White (in part), 1874, U. S. Geog. Surveys W. 100th Mer.; Prelim. Kept. Invertebrate Fossils, 

 pp. 9-10. (Described as a new species, including specimens referred to both Lingulella manticula and L. arguta.) 



Lingula manticula White (in part), 1877, U. S. Geog. Surveys W. 100th Mer., vol. 4, pt. 1, p. 52, PI. Ill, fig. 2b (not 

 fig. 2a). (Described essentially as in the preceding reference and discussed. The specimen represented by fig. 

 2b could not be located when the drawings of this species were being made, and the original drawing is reproduced 

 in this monograph, PI. XX, fig. Ic. The specimen represented by fig. 2a is referred in this monograph to Lingu- 

 lella arguta.) 



Not Lingula? manticula Waloott, 1884, Mon. U. S. Geol. Survey, vol. 8, pp. 13-14, PL IX, fig. 3; and PL XI, fig. 2. 

 (These specimens are now referred to Lingulella punctata.) 



Shell small, general form elongate ovate, with the ventral valve subacuminate, and the 

 dorsal valve ovate m outline. Valves rather strongly convex, the ventral being slightly more 

 so along the posterior half than the dorsal. There is some variation in the outline of the valve, 

 as is shown for the ventral by Plate XX, figures 1 and Ic, and for the dorsal by Plate XX, figures 

 la and lb. 



Surface of shell marked by fine concentric lines of growth and very fine, slightly irregular 

 concentric strife ; when the outer shell is partly exfohated the outer surface of the inner layers 

 is marked by fine, concentric lines and not very distinct radiating striae; the inner surface of the 

 shell shows concentric lines of growth and a few scattered pits or punctse. The shell is of 

 medium thickness and formed of a thm outer layer and one or' more inner layers or lamella. 



The average length of the ventral valve is 3.5 mm.; width, 2 mm. The associated dorsal 

 valve of the same width has a length of 3 mm. 



As shown in tlie cast of the interior of the shell the area of the ventral valve is long, clearly 

 defined, and broken midway by a narrow but strong pedicle groove. It is also marked near its 

 lateral margins by narrow flexure lines. The strise of growth cross the area parallel with its 

 base. They are very distinct but do not show on the cast of the pedicle furrow. 



The cast of the interior of the ventral valve shows the visceral cavity (v) and the outline of 

 the heart-shaped pit (x). In the dorsal valve sufficient is shown to indicate that the visceral 

 cavity extended forward to about the middle of the shell, and that a narrow median septum was 

 present. 



Observations. — This is a small species that is representative of quite a group of somewhat 

 similar forms that occur in the Upper Cambrian and Lower Ordovician faunas, both in the 

 Rocky Mountain and Appalachian regions; Lingulella punctata (Walcott) representing the group 

 in the Rocky Mountains, and L. desiderata (Walcott) in the Appalacliian region. 



Of the figures given by Wliite [1877, PI. Ill] figure 2b is taken as the type. Figure 2a of 

 Wliite [1877, PI. Ill] is a larger shell, which I have referred to L. arguta. The specimens identified 

 by Walcott [1884b, p. 13] as "Lingula? manticula" have been referred to L. punctata, as a 

 comparison with the type of " L. f manticula" "VYliite shows them to be distinct. 



This species was referred to the "Quebec group" by WIrite [1874, p. 9], and it is probable 

 that the horizon at which it occurs will be found to be in the passage beds between the Upper 

 Cambrian and Lower Ordovician, or what corresponds to the lower part of the Pogonip limestone 

 of the Eureka, Nevada, section. Since the preceding was written, Spurr collected a few Cam- 

 brian fossils in southern Nevada among which occurs a form that appears to be identical with 

 L. manticula. The fragments of trilobites indicate a Cambrian fauna but not its stratigraphic 

 horizon. 



Formation and locality. — Lower Ordovician: (202) Pogonip limestone, on the summit of the ridge directly 

 southeast of the Jackson mine, northwest of Shadow Canyon, Eureka district [Hague, 1892, Atlas], Eureka County; 

 and (214b) limestone near the middle of the Pogonip limestone, White Pine district. White Pine County; both in 

 Nevada. 



Upper Cambrian: (8e) Limestone in Patterson Cauyon, west side of the Schell Creek Range; (313f) limestone at 

 Schellbourne, Schell Creeh Range, and (8f) limestone at summit of canyon, 10 miles (16.1 km.) south of Egan Canyon, 

 east side of Egan Range; all in AMiite Pine County, Nevada. 



