52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



sections reveal no such lateral plates. Some specimens of this and other 

 species of stenoscismataceans have short fractures in the beak region, 

 some arranged nearly symmetrically, equidistant from the median 

 septum. A cross-section normally reveals these as fractures, not plates, 

 because they appear only as thin dark lines. Perhaps such lateral frac- 

 tures account for the auxiliary plates in Stainbrook's drawings. 



Occurrence and abundance. — Upper part of the Callaway Forma- 

 tion, 1.5 mile SE. of Danville, Montgomery County, Mo. (53 speci- 

 mens USNM 141852) ; upper part of the Callaway Formation, branch 

 of Whippoorwill Creek, about 5 miles S. of New Florence, Mo. (43 

 specimens USNM 141853) ; upper part of Callaway, in stream bed, 

 NE.J4 sec. 13, T-46-N, R-6-W, 2 miles N. of Danville, Mo. (13 

 specimens USNM 141854) ; upper part of Callaway, on Missouri 

 Highway 19, one mile N. of Big Spring, Mo. (4 specimens USNM 

 141858) ; Cedar Valley Limestone (Cranaena iowensis zone), Mid- 

 river, Johnson County, Iowa (1 specimen USNM 141861); Cedar 

 Valley (C. iowensis zone) Lost Creek, 2 miles S. of old State Quarry, 

 on W. side of Cedar River, Iowa (1 specimen USNM 141862) ; Cedar 

 Valley, SW.}4 SE.^, 15, T-77-N, R-2-E, Buffalos Twp., Scott 

 County, Iowa, on Dodges Creek (33 specimens USNM 141859) ; 

 Cedar Valley, NE.% NE.^, sec. 26, T-17-N, R-2-E, Andalusia, 111. 

 (8 specimens USNM 141860) . 



Age. — Late Middle Devonian, in the Callaway Limestone and the 

 correlative part of the Cedar Valley Limestone. 



ATRIBONIUM HALLI (Fagerstrom) 



Stenoscisma halli FAGERSTROM, J. A., 1961, Journ. Paleont. vol. 35, No. 1, 

 p. 29, pi. 9, figs. 48-51, (not Camarophoria rhomboidalis HALL AND 

 CLARKE, 1894 ; HALL, 1894) . 



Stenoscisma rhomboidalis (Hall and Clarke) FAGERSTROM, J. A., 1961, 

 Journ. Paleont. vol. 35, No. 1, p. 29, pi. 9, figs. 45-47, (not Camarophoria 

 rhomboidalis HALL AND CLARKE, 1894; HALL, 1894). 



Discussion. — The little specimens from Formosa, Ontario, which 

 Fagerstrom (1961) equated with Camarophoria rhomboidalis Hall 

 and Clarke have the generic characters of Atribonium. Their sub- 

 trigonal outline, short and weak costae, and especially their flattened 

 anterior surfaces are characteristic features. They differ from all other 

 known species of the genus in having few (two or three) costae on 

 the fold, and normally the same or a greater number on each flank. 

 These specimens differ from Hall and Clarke's Indiana species (here 

 assigned to the genus Coledium n. gen.) in their smaller size, lower 

 convexity, trigonal rather than ovate outline, weaker costae that begin 

 farther anterior, and especially in their geniculation of each valve to 

 produce the characteristic flattened anterior of Atribonium. 



