52 
GEOLOGY 
concave mesial hollow in the dorsal valve, and a smaller, undefined, rounded, mesial ridge in the ventral valve. 
Beak of the dorsal valve tumid, incurved, small, with a moderate opening at the apex. Surface smooth, with a 
few distinct imbricating lines of growth. (See : Fossiles du Carbonifere de Belgique, p. 300.) 
Locality. — The specimen figured was found near Great Salt Lake city in company with the 
two last species of Terebratula described. Lerou.x gave me some also, from the vicinity of El 
Paso, Chihuahua, and from the headwaters of the Rio Colorado Chiquito. 
Explanation of figures. — Plate VI. fig. tO, 10 a, 10 b. Different views of Great Salt L,ike .specimen. 
TEREBRATULA PLANO-SULCATA Phill. 
Plate VI , fig. 8 , 8a, 8 b. 
Bescriplion. - Shell pentahedral, depressed, middle of each valve plano-sulcate. (See: Fossiles du Carbonifere 
de Belgique, p. 301; and Geology of Yorkshire, Pari II, the Mountain Limestone district, p. 220.) 
Locahty. — This well known species of the Mountain Limestone of Europe is also found in the 
States of Ohio, Indiana, Illinois, Kentucky and Arkansas. I have met with it at Tigeras, New 
Mexico, where it is quite common. 
Explanation of figures. — Plate VI, fig. 8, 8a, 8 b. Different views of Tigei'as specimen. 
TEREBRATULA SUBTILITA Hall. 
Plate VI , fig. 9,9a, 9b, 9c, 9 d , 9 e , 9 f. 
Description. — Shell sub-orbicular, more or less gibbous; lateral and front margins in one plane, except near 
the front margin , where a contorted sinus becomes developed with a corresponding concave mesial hollow in the 
dorsal valve. The hollow begins generally at a third of the length from the beak ; sometimes very near the beak 
(see fig. 9 e) , and sometimes near the front margin. The ventral valve has a large mesial ridge corresponding , 
broadly rounded; sometimes indistinct and even with a little depression in the middle (see fig. 9 a). Surface smooth, 
marked by imbricating lines of growth. Beak of the dorsal valve small, incurved, with quite a large opening at 
the apex. 
Observations. — This species is variable in its characters, and its name of subtilifa is very appro- 
priate. It was first found on the banks of the Missouri, near Weston, by Capt. Stansbury (See: Ex- 
ploration of the Great Salt Lake, Paleontology, p. 409; pi. 11, fig. 1, la, lb, 2, 2a, 2b, 2c.). It has 
since been recognized in the Carboniferous rocks of the States of Illinois, Indiana, Kentucky and Ar- 
kansas. Its general form resembles rather the Terebratula; section Jugatee of the Secondary epoch, than 
the Terebratulw of the Paleozoic rocks. 
Locality. — Occurs in great abundance in the Mountain Limestone of the Rocky mountains , of 
the Sierra Madre , of the Sierra de Mogoyon , and in the vicinity of Great Salt Lake. I have seen 
several thousand specimens of this species at Tigeras, at Pecos village, on the summit of the Si- 
erra de Sandia, and the Sierra de Mogoyon. I have received it from the vicinity of El Paso, 
Chihuahua; from the junction of the rivers San Pedro and Gila, Arizona; from the sources of the 
Rio Colorado Chiquito; the Great Salt Lake; Shasta county in California; and finally from the south- 
ern coast of Vancouver island. 
Explanation of figures. — Plate VI, fig. 9,9 a. Specimen showing the sinus on both valves. 
» - VI, fig. 9 b, 9 e. Larger specimen, more elongated. 
» VI, fig. 9 d, 9 e, 9 f. Very gibbous and elongated specimen. 
These three specimens were found at Pecos village , New Mexico. 
ZAPHRENTIS STANSBURYl Hall. 
Plate VII , fig. 7. 
Description. — Corallum curved, somewhat elongated, and encircled with a few well marked constrictions. Ca- 
liee circular, deep, with a thin margin. Fossula situated toward the dorsal side, or large curve of the corallum. 
Septa numerous , lamellate , thin , extending to the edge of the fossula. 
