FORMATION'S AND FOSSILS OF SOUTH MANCHURIA 113 



concave border. It is moderately convex, rounded triangular in out- 

 line, and has a poorly defined, rather slender axis, which is wide at 

 the anterior end, tapering rather rapidly to the posterior end. 

 Pleural lobes rather convex and sloping gradually into the marginal 

 border without any well-defined boundary. Axes and pleural lobes 

 are marked very slightly by scarcely traceable slender ribs. 



Formation and locality. — Middle Ordovician, Ssuyen formation: 

 In the lower fossil horizon of the black-banded limestones, near Tou- 

 fang-kou, 2.5 miles northwest of Pen-hsi-hu, Liao-tung, Manchuria. 



Genus NILEUS Dalman, 1826 



NILEUS WALCOTTI, new species 



Plate 39, Figuee 10 



A single but very remarkable cephalon to which is attached six 

 thoracic segments occurs in Louderback's collection from Shensi, 

 China. 



Description. — Cephalon nearly semicircular, length a little less 

 than half of the width, strongly and evenly convex, sloping gently 

 to the sides without any depressed border. Eyes very large, closely 

 covered with minute tubercles as shown under a low-power magnify- 

 ing lens, their length about half the whole length of the cephalon. 

 The distance between the posterior corner of the eye and the posterior 

 margin of the cephalon is a little less than that between the eye and 

 the frontal margin. The glabella is not differentiated from the re- 

 mainder of the cephalon. The facial suture extending from tht 

 anterior corner of the eye first curves outward and then inward, 

 closely encircling the front margin. Behind the eye it runs slightly 

 outward, cutting the posterior margin at a point just back of the 

 eye. The surface of the test is apparently smooth. Thoracic seg- 

 ments are strongly convex, and the axial furrows are slightly 

 impressed. 



The specific name is given in honor of Dr. Charles D. Walcott, 

 former secretary of the Smithsonian Institution, who described a 

 great number of the Chinese fossils. 



G omparison. — I am not acquainted with any American or Euro- 

 pean species with which this form is likely to be confounded, but it 

 may be compared with Nileus perkinsi Kaymond from the upper 

 Chazyan strata on Isle La Motte, Vt., North America. The com- 

 paratively anterior position of the eyes, the rather broad free cheek, 

 and smooth surface of the test, however, serve readily in distin- 

 guishing it. 



Formation and locality. — Ordovician: Near Ning-kiang, Shensi, 

 China. 



Holotype.—\].S.'E.M. No. 83770. 



