81() I'llOVEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



scars, a narrow nu>diau septum, and faintly impressed main vascular 

 sinus that curves outward and forward at al)out one-third the distance 

 from the out(n- margin to the median septum; the central nuiscle scars 

 are small and situated l)ack of the center of the valve on each side of a 

 low median swelling on which the median septum oocurs; the position 

 of the anterior lateral umscle scars is indicated at the end of the median 

 septum a little in advance of the center of the valve. 



OIm;rvatl<ms. — This minute shell has the generic characters of D!cel- 

 loriixs pol/txK, but it differs specifically in minute size and the positions 

 of the muscle scars in the dorsal valve. 



Formation and locality. — Middle Caml)rian. Chang Hsia limestone. 

 Two and oiu>-half miles southwest of Yen Chuang, Shantung, China. 



Also from a river di'ift block one mile south of Chen Ping Hsien, on 

 the Lan llo liiver, southern Shensi. 



Collections of Bailey Willis and Eliot T. Blackwelder, Carnegie 

 Institution Expedition to China. 



DICELLOMUS PECTENOIDES Whitfield. 



OholiiH iHcUiioidcx WiiiTiaELi), Ludlow's Kept. KeconnaiHSixiice Black Hills of 



Dakota, 1.S75, p. 103, figs. 1, 3. 

 Ohulus? pecteiioUh's Whitfield, Geo!, aiul (Tei),g. Surv. Kocky IMountain region, 



Powell, 1880, p. 328, pi. ii, figs. 18, 19. 

 Oholelld. ])frtrii(>t(li'ff Schuchert, Bull. U. S. Geol. Survey, No. 87, 1897, p. 275. 



This is the largest shell of the several species of the genus. A 

 ventral valve 1> nmi. long has a width of 11 nun. All that is known of 

 the structure of the shell indicates that it was like D. politiis. This 

 species differs from all the other species by the anterior iDosition of 

 the central nmscle scars of the dorsal valve, and its larger size. 



Foriiaitloii and Joixdity. — Middle Cambi'ian. Deadwood sandstone, 

 Castle County, on west side of the Black Hills; also at Deadwood, in 

 the cliffs on the east side of the valley. South Dakota. 



DICELLOMUS POLITUS Hall. 



Oholus appolinm Owen (not Eichwald), Geol. Surv. Wisconsin, Iowa, and 



Minnesota, 1852, ]il. i u, figs. 9, 11, 15, 20. 

 Lingula ! jyolita Hall, Ann. Kept. Geol. Surv. Wisconsin, 1861, p. 24; Geol. 



Kept, Wisconsin, I, 1862, pp. 21, 435. 

 OlxiJrIld ? polUa Hall, Sixteenth Ann. Kept. New York State Cab. Nat. Hist., 



1863, p. 133, pi. VI, figs. 17-21; Trans. Albany Institute, V, 1867, p. 112. 

 Liugalepii^ prrima Meek and Havden, Smithsonian Contrb. to Knowl., XIV, 



1864, No. 172, p. 3, pi. i, fig. 2. 



Diccllorims j'olila Hall, Twenty-third Ann. Kept. New York State Cab. Nat. 



Hist., 1873, p. 246. 

 Oholdla politit Whitfield, Geol. and Geog. Surv. Kocky Mountain Region, 1880, 



p. 339, jil. II, figs. 12, 13. 

 OboJdla poUla Walcott, Bull. U. S. Geol. Survey No. 30, 1886, p. 111. 



