74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 48 



of brachial valve; deltidial plates not observed; foramen small, sub- 

 circular, perforating apex of beak. 



Brachial valve more strongly convex, outline subcircular; beak 

 short, blunt, apex within pedicle valve. 



Pedicle valve interior with one small hinge tooth on each side ; den- 

 tal plates bowed outwardly, reaching valve floor, extending forward 

 one-third to one-half length of valve, nearly meeting one another on 

 posterior floor, there slightly thickened to form sessile spondylium, 

 bases of plates converging anteriorly, meeting at anterior edge of 

 spondylium of some specimens but not joined to form septum. Muscle 

 and pallial marks not observed. 



Brachial valve interior with undivided hinge plate extending for- 

 ward about 1 mm. ; crura extending forward from anterior edge of 

 plate ; median septum strong, rather low, height increasing anteriorly, 

 extending about one-third valve length ; camarophorium narrow, flatly 

 concave, widening toward anterior, posterior half with short inter- 

 camarophorial plate braced to underside of hinge plate in apex, then 

 declining anteriorly. 



Lectotype (here designated) . — Weller, 1914, plate 23, fig. 57 (Wal- 

 ker Mus., Univ. Chicago, No. 13937). 



Comparisons. — Sedenticellula hamburgensis is characterized by its 

 small size, rotund outline, simple costae, flattened posterolateral areas 

 on the pedicle valve outlined by sharp beak ridges, and its completely 

 sessile spondylium. These features distinguish it from the only other 

 known species, S. sacra n. sp. 



Occurrence and abundance. — Hamburg Oolite of Weller (1906), 

 shore of Mississippi River y 2 mile north of Hamburg, 111. (8 speci- 

 mens USNM 89886) ; Hamburg Oolite, Irish Hollow, just east of 

 Hamburg, Calhoun County, 111. (23 specimens USNM 142021) ; plas- 



J K L M N 



Fig. 14. — Sedenticellula hamburgensis (Weller), Kinderhook, Hamburg, 111.; 

 sections by Weller (1914, p. 170, fig. 2, B, D, F-H, J-S) X3V 4 ; A-I, brachial 

 valve ; J-O, pedicle valve showing sessile spondylium. 



