DESCRIPTION OF GENERA AND SPECIES. 283 



Plectorthis willisi Weller (plate 25, figs. 10, n). 



1907. Plectorthis willisi Weller, Proc. U. S. Nat. Mus., vol. xxxn, p. 557. 



Shell transversely subelliptical in outline, the hinge-line a little shorter than 

 the greatest width, cardinal extremities slightly rounded. Pedicle valve depressed- 

 convex, slightly compressed toward the cardinal extremities; the beak small, scarcely 

 incurved, cardinal area a little concave, sloping backward at an angle of about 40 to 

 the plane of the valve; cardinal margins angular. Brachial valve nearly as convex 

 as the pedicle, compressed toward the cardinal extremities. Surface of each valve 

 marked by from 20 to 25 major radiating, rounded costae, which increase in width 

 conspicuously in passing from the beak to the front margin; in each interspace 

 between these major costse from one to three smaller ones which do not reach the 

 beak are intercalated. The more minute surface markings are destroyed. The 

 dimensions of a pedicle valve are: length 7.5 mm., width 12 mm., height of area i 

 mm., convexity 2 mm. 



The most notable feature of this shell is the conspicuous broadening of the 

 major costae in passing from the beak to the front margin. 

 Dalmanella testudinaria (Dalman) (plate 25, figs. 12-16). 



1828. Orthis testudinaria Dalman, Kongl. Svenska Vet.-Skad. Handl. for 1827, p. 1 15, plate 2, fig. 4. 



1847. Orthis tesludinaria Hall, Pal. N. Y., vol. I, p. 117, plate 32, fig. i ; p. 288, plate 79, fig. 4. 



1863. Orthis testudinaria Billings, Geol. Canada, p. 165, fig. 144. 



1869. Orthis testudinaria Davidson, Brit. Sil. Brach., vol. in, p. 226, plate 28, figs. 13-24. 



1882. Orthis testudinaria Whitfield, Geol. Wis., vol. iv, p. 258, plate 12, figs. 5-7. 



1884. Orthis testudinaria Walcott, Monog. U. S. G. S., vol. vin, p. 72, plate 1 1, fig. 10. 



1892. Dalmanella testudinaria Hall and Clarke, Pal. N. Y., vol. vin, pt. i, pp. 190, 206, 218, 224, plate 



5B, figs. 27-39. 



1893. Orthis (Dalmanella) testudinaria Winchell and Schuchert, Minn. Geol. Survey, vol. in, pt.ni, pp. 



177,241- 



1897. Orthis testudinaria Sardeson, Am. Geol., vol. xix, p. 92. 

 1903. Dalmanella testudinaria Weller, Pal. N. J., vol. in, p. 155, plate 10, figs, i, 2. 



This species is one of the most widely distributed brachiopods found in strata of 

 Ordovician age, it being recognized throughout the world wherever middle Ordo- 

 vician strata are known. In the fauna of the Ki-sin-ling limestone it is the most 

 abundant species. The specimens agree well with representatives of the same spe- 

 cies from North America, but are, on the average, perhaps, slightly more elongate. 

 The average size of the specimens in the collection is about 13 mm. in length and 14 

 mm. in width. 

 Dalmanella subaequata (Conrad) (plate 25, figs. 19, 20). 



1843. Orthis subcequata Conrad, Proc. Acad. Nat. Sci. Phila., vol. I, p. 333. 



1847. Orthis subaquata Hall, Pal. N. Y., vol. I, p. 118, plate 32, fig. 2. 



1862. Orthis sub&quata Hall, Geol. Wis., vol. I, p. 42, figs. 1-3, and p. 436. 



1892. Dalmanella subaqnata Hall and Clarke, Pal. N. Y., vol. vin, pt. i, pp. 194, 207, 224, plate 50, figs. 



6-1 1. 



1893. Orthis (Dalmanella) subczquata Winchell and Schuchert, Minn. Geol. Surv., vol. in, p. 446, plate 



33, figs. 30-36. 

 1903. Dalmanella subcequata Weller, Pal. N. J., vol. in, p. 156, plate 10, figs. 3-4. 



In North America this species is a variable one, no less than four named varieties 

 being recognized by Schuchert in his "Synopsis of American Fossil Brachiopoda." 

 The Chinese specimens are entirely similar to American ones and agree for the most 

 part with the typical form of the species, though some of those with slightly coarser 

 costse might perhaps be referred to the variety pervetus. The gibbosus variety with 

 well-developed sinus has not been detected in the Chinese collection. 



Clitambonites chinensis Weller (plate 25, figs. 17, 18). 



1907. Clitambonites chinensis Weller, Proc. U. S. Nat. Mus., vol. xxxii, p. 558. 



Shell broader than long, the hinge-line straight, the greatest width at the hinge- 

 line or a little in front of it, the lateral and anterior margins describing a regular 



