OBOLID^. 387 



Obolxjs chinensis (Walcott). 

 Plate XXXIX, figvires 7, 7a-b. 



Obolus (Lingulella) chinensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 328-329. (Described and discussed 

 as below as a new species.) 



General form broadly subovate, with the ventral valve broadly subacuminate and the dorsal 

 valve oval, with the posterolateral slopes somewhat straightened. There is some variation 

 in the proportions of width and length in different shells. Valves rather strongly convex for 

 so thin a shell, in this respect resembling species of Dicellomus. Surface marked by fine con- 

 centric strise and lines of growth and very fine undulating concentric lines; this outer surface 

 is usually a dull black and adheres to the matrix; when the outer layer is exfoliated the surface 

 is shiny black and marked by numerous radiating striae in addition to concentric strise; the 

 inner surface shows a few scattered punctse in addition to radiating and concentric strise out- 

 side the visceral area. The shell is of medium thickness and formed of a thin outer layer and 

 several inner layers or lamellse that are slightly oblique to the outer layer; the lamellse are more 

 numerous and more oblique to the outer layer over the anterior and anterolateral portions 

 of the shell. The ventral valves average 3 mm. in length, with width varying from 2 mm. to 

 2.5 mm. The dorsal valve is slightly shorter than the ventral when the two valves have the 

 same width. 



The interior of the ventral valve shows that the area is short and divided midway by 

 a narrow pedicle furrow that merges into the visceral area which extends forward about one- 

 third the length of the valve; on each side of the anterior central portion of the visceral area 

 there are two small trapezoidal areas within which the central scars and the middle and out- 

 side lateral muscle scars were attached ; the small transmedian and anterolateral muscle scars 

 are situated close to the main vascular sinus opposite the anterior portion of the central visceral 

 area. A partial cast of the interior of the dorsal valve shows a rather wide visceral area with 

 the anterolateral scars about the center of the valve and the central scars about one-fourth 

 of the distance back from the center to the posterior margin. Of the impressions left by the 

 vascular system only the main vascular sinuses of the ventral valve have been seen. These 

 are situated about midway between the central visceral area and the margins of the valve. 



Oiservations. — This species occurs abundantly in association with Acrotreta shantungensis 

 Walcott. It is closely related in form to Oholus prindlei (Walcott) of the upper Olenellus 

 zone of eastern New York, and belongs with a group of small shells that have a wide vertical 

 and geographic range, as is noted under the description of 0. prindlei. With the data available 

 for comparison it differs from 0. prindlei in its shorter cardinal area, and visceral area in the 

 dorsal valve. From Lingulella damesi (Walcott) it differs in being broader in proportion to 

 its length. 



Formation and locality. — Middle Cambrian: (C62) Earthy layer in the middle limestone of the Kiulung 

 group [Blackwelder, 1907a, pp. 37 and 40 (last list of fossils) and fig. 10 (base of bed 7), p. 38], 2.5 miles (4 km.) south 

 of Yenchuang, on the north-northeast spur of Hulushan, Sintai district. Shantung, China. 



I Obolus complexus Barrande. 



Plate XII, figures 8, 3a, 8, 8a. 



Obolus? complexus Barrande, 1879, Systeme silurien du centre de la Boheme, vol. 5, pt. 1, PI. XCV, figs, iii: 1-2; 



PI. CXI, figs, vi: 1-2; PI. CXIII, fig. v; and PI. CLII, fig. ii: 4. (No text reference. PL XII, figs. 3, 3a, 8, 



and 8a, of this monograph are copied from PL CLII, fig. ii:4A; PL CXIII, fig. v:A; PL XCV, figs, in: lA-B; 



and PL XCV, fig. iii:2C, respectively.) 

 Obolella ?? complexity Barrande, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 73, fig. 



31. (Merely suggests change in generic reference. Fig. 31 is copied from Barrande, 1879b, PL CLII, fig. n:4A.) 

 Schmidtia?? complexus Barrande, Mickwitz, 1896, M6m. Acad. imp. sci. St.-P6tersbourg, 8th ser., vol. 4, No. 2, pp. 



19-20. (Generic relations discussed in German.) 



Barrande [1879b] recognized the relations of this species to Oholus, although at the time 

 he did not have the results of Mickwitz's studies to aid him. The latter [1896, p. 19] considers 



