SIPHONOTRETID^. 613 



radiating outward from the base of the foramen. Fine transverse strise cross the narrow area 

 and then incurve and cross the pseudodeltidium. 



The dorsal valve has a well-defined area, with an obscure pseudodeltidium parting it mid- 

 way. The cast of the interior of the valve sliows two broad, shear-shaped divero-ino- rido-es 

 that extend from near the apex to the center of the shell. Numerous vascular markings extend 

 outward from the ridges. These ridges may indicate the muscular scars or merely the main 

 trunks of the vascular depressions. The surface of the area is marked by fine transverse strife 

 that abruptly incurve toward the front of the area, so as to follow along its anterior margin 

 to the pseudodeltidium. 



The surfaces of both valves, as shown in the casts, are smooth, except where marked by 

 concentric lines of growth. 



Shell substance unknown, but probably calcareous. It is dissolved away in all the speci- 

 mens in the collection, only the impression of the shell remaining in the decomposed arenaceous 

 limestone. 



This species occurs in abundance, associated with Nisvsia festinata, Hyoliihes americanus, 

 and fragments of Olenellus. 



The specific name was given in honor of Mr. Atreus Wanner. 



Formation and locality. — Lower Cambrian: (49) Sandstone on Codorus Creeh 0.125 mile (0.2 km.) beloiu Meyer's 

 mill, near Emigsville; and (49a) sandstone on the Liverpool road, south of the schoolhouse, 3 miles (4.8 km.) northwest 

 of York; both in York County, Pennsylvania. 



Specimens that are somewhat doubtfully referred to this species occur at the following 

 localities : 



Lower Cambrian: (2o) Limestone bowlders in conglomerate, on shore at east entrance to harbor at Bic, Rimouski 

 County, Quebec. 



(7) Shaly beds about 1,000 feet (305 m.) above the quartzitic beds, Silver Canyon, 'WTiite Mountain Range, Inyo 

 County, California. 



YORKIA? WASHINGTONENSIS Walcott. 



Plate LXXXII, figures 2, 2a. 



Yorhiaf wasUngtonensis Walcott, 1897, Proc. U. S. Nat. Mus., vol. 19, pp. 715-716, PI. LX, fig. 3. (Described and 

 discussed as below as a new species. The specimen represented by fig.. 3 is redrawn in this monograph, PL 

 LXXXII, fig. 2.) 



Ventral valve longitudinally ovate, depressed, convex. Area and pseudodeltidium invisi- 

 ble, but, from the character of the foramen and its resemblance to the foramen of Y. wanneri, 

 it is probable that the area was somewhat similar to the area of that species. The cast of 

 the interior of the ventral valve shows a rather long, large foramen, in advance of which two 

 ridges (vascular trunks) diverge somewhat as in the ventral valve of Y. v;anneri Walcott 

 (p. 612). There is also present a short longitudinal depression in the cast, which indicates 

 a corresponding mesial ridge just in advance of the foramen. The surface of the interior of the 

 shell is marked by fine concentric lines and very fine interior ridges. Shell substance appar- 

 ently corneous. 



This species is founded upon two partial casts of the ventral valve, preserved in com- 

 pact gray limestone. The shell appears to be very tliin over the outer portions and thick 

 over the umbonal region. 



The generic reference is somewhat doubtful. Oholella is suggested by the cast of the 

 pedicle tube, also Trematoholus. The pedicle tube and form of the vascular trunks suggest 

 YorMa, wliile tlie shell substance is more like that of Botsfordia. 



The specific name is derived from Washington County, New York. 



Formation and locality. — Lower Cambrian: (37b) Limestone 0.25 mile {0.4 hm.) east of Salem, Cambridge 

 quadrangle ( U. S. Geol. Survey), Washington County; (338n) western belt of conglomeratic limestone, Rensselaer 

 County; and (38a) limestone 2 miles (3.2 km.) south of North Granville, on the road which turns south from the road 

 running between that village and Truthville, 4 miles (6.4 km.) west-northwest of Granville, Fort Ann quadrangle 

 (U. S. Geol. Survey), Washington County; all in New York. 



