366 Eepoet of the State Geologist. 



Conchidium exponens. 



Plate 10, figs. 20-23. 



Conchidium exponens, Hall. PalaeoHtology of N. Y., vol. VIIl, pt. 2, expl. 

 pi. Ixvi, figs. 6-9. 1894. 



Shell elongate, subtriangular in marginal outline ; valves subse- 

 quently convex. Median fold distinct over the anterior region 

 of the pedicle- valve. Surface with numerous fine, rounded plica- 

 tions which are more or less obsolete over the lateral slopes and 

 umbonal region of the valves. The pedicle-valve bears a spondy- 

 lium extending less than one-half its length, while in the brachial 

 valve the septal plates do not unite. 



Niagara group. Louisville^ Kentucky, 



Conchidium scoparium. 



Plate 11, figs. 8, 9. 



Conchidium scoparium, Hall. Palaeontology of N. Y., vol. VIII, pt. 2, expl. 

 pi. Ixvii, figs. 6, 7. 1894. 



Shell with biconvex valves; marginal outline subcircular. 

 Pedicle-valve with prominent, suberect umbo, slightly incurved 

 at the top, with gradually expanding sides, fc^urface without 

 median fold or sinus, but covered with numerous fine plications. 



Guelph dolomites. Durham^ Ontario. 



Conchidium obsoletum. 



Plate 11, figs. 1, 2. 

 Conchidium obsoletum, Hall. Palaeontology of N. Y., vol. VIII, pt. 2, expl. 

 pi. Ixvii, figs. 8, 9. 1894. ' 



Shell with highly convex valves and greatly flattened cardinal 

 slopes. Anterior margin broadly curved, subtransverse. Surface 

 with a few obscure and broad plications, obsolete at the sid^s of 

 the valves. 



Niagara dolomites. Genoa, Ohio. 



Conchidium Nettelrothi. 



Plate 10, figs. 24, 25. 



Pentamerus Knighti, Nettelroth, Kentucky Fossil shells, p. 57, pi. xxix, figs. 



1, 2, 17. 1889. 

 Conchidium Nettelrothi, Hall. Palaeontology of N. Y. , vol. viii. pt. 2, p. 234, 



foot-note. 



