no 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



longitudinally along fold, greatest swelling in umbonal region; beak 

 bluntly pointed, apex normally hidden beneath pedicle beak. 



Pedicle valve interior with dental plates joining above floor to form 

 rather shallow spondylium, supported for entire length by median 

 septum (spondylium not sessile in apex of valve), height of septum 

 increasing anteriorly, becoming very high for genus, continuing anteri- 

 orly about one-third length of valve. 



Brachial valve interior with short undivided hinge plate ; cardinal 

 process formed by slight swelling of apex of plate, weakly scored lon- 

 gitudinally for attachment of diductor muscles; camarophorium ele- 

 vated on low median septum duplex in apex, height of septum in- 

 creasing greatly toward anterior; sides of camarophorium reaching 

 nearly to underside of hinge plate, midline connected to plate by inter- 

 camarophorial plate extending anteriorly slightly beyond hinge plate ; 

 septum of camarophorium extending anteriorly about one-fourth length 

 of valve, crest of camarophorium somewhat longer; crura extending 

 forward from anterior edge of hinge plate, curved ventrally to follow 

 contour of crest of camarophorium; muscles and pallial marks not 

 observed. 



Holotype.— USNM 142109, pi. 17, fig. 2. 



Comparisons. — Coledium dutroi is the largest known species of the 

 genus, comparable in size to many species of the normally larger 

 Stenoscisma. In addition to its size, it is characterized by its high con- 

 vexity (in large adults) broad fold that becomes high in adults and 

 has a median groove in about half the known specimens, its broad 



Fig. 25. — Coledium dutroi n. sp., Mississippian Ladrones Ids., Alaska, trans- 

 verse sections X4, original length 20.0 mm. USNM 142110, distances given from 

 pedicle valve beak. 



A. 2.5 mm. : cardinal process distinct, septum of spondylium high. B. 2.8 mm. : 

 spoon of camarophorium separate from hinge plate, septum duplex with wedged 

 insertion into valve floor. C. 3.0 mm. : intercamarophorial plate duplex. D. 3.4 

 mm. E. 4.0 mm. : crura and intercamarophorial plate anterior to hinge plate ; 

 spondylium high. 



