NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA GRANT III 



Table 20. — Measurements of Coledium dutroi, from the Mississippian of Alaska 



Measurements, in millimeters 



sulcus also with median groove in many, and by its nearly complete 

 lack of costation. Internally, the septum of the spondylium is usually 

 high, elevating the spondylium nearly to the middle of the height of 

 the valve, and consequently the spondylium is not as deep as normal 

 for most stenoscismatids. It is named for J. T. Dutro, Jr., U.S. Geo- 

 logical Survey, who provided the Alaskan specimens of this species, 

 and of species of Camerisma. 



Only three other species resemble C. dutroi. One that approaches 

 it in size is C. therum (Walcott) from the Mississippian of Nevada. 

 Despite its large size for the genus, C. therum attains a maximum size 

 only about half that of C. dutroi. In addition, C. dutroi differs in its 

 broader fold, absent or nearly absent costae, and only slightly pro- 

 truding valve edges. C. erugatum n. sp., also Mississippian, is entirely 

 smooth, but C. dutroi attains a much greater maximum size, its fold is 

 broader and, in all but large adults, is lower ; furthermore, many speci- 

 mens of C. dutroi have a median groove along the midline of the fold 

 and sulcus. 



C. crassum (Hamlet) from the Permian of Timor attains a size simi- 

 lar to that of C. dutroi, but differs in its more equilaterally pentagonal 

 outline, proportionately broader, flatter crested fold, occasional weak 

 costae near the anterior of the fold, more swollen brachial umbo, much 

 shorter pedicle beak, and its nonprotruding anterior and anterolateral 

 valve edges (see pi. 18, fig. 6). 



Occurrence and abundance. — Unnamed Upper Mississippian lime- 

 stone of Condon (1961), Craig Quadrangle, Southeastern Alaska, all 

 specimens collected by G. H. Girty in 1918: U.S.G.S. loc. 3747, dark 

 brittle limestone on south shore of Shelikof Island, one specimen 

 (USNM 142110) ; U.S.G.S. loc. 3703, near middle of white limestone 

 on east shore of island No. 250 in Ladrones Islands, three specimens 

 (USNM 142109, 142111, 142112) ; U.S.G.S. loc. 3767, on east shore 

 of island No. 250 in Ladrones Islands, three specimens (USNM 

 142107,142108,142113). 



