370 Hepoet of the State Geologist. 1 , ' 



Sieberella Roemeri. 



P:ate 13, fig. 4. 



Pentamerus galeatus, F. Roemer. Silur. Fauna des westl. Tennessee, p. 73, 



pi. V, fig. 11. 

 Sieberella Roemeri, Hall. Palaeontology of N. Y., vol. VIII, pt. 2, p. 247, pi. 



Ixxii, fig. 6. 1894. 



Shell similar in general aspect to Sitlerelld galeaia, but some- 

 what more elongate, less distinctly plicate and always smaller, 

 having, also, the septal plates of the brachial valve united, form- 

 ing a cruralium resting on a median septum. 



Magara group. Ferry county^ Tennessee. 



Rensselaeria Cayuga. 



Plate 13, figs. 14, 15. 



HensselcBria Cayuga, Hall. Palaeontology of N. Y., vol. VIII, pt. 2, p. 370, 

 pi. Ixxv, figs. 1, 2. 1894. 



Shell lenticular, often of large size; suboval in marginal out- 

 line. Yalves subequally biconvex, sloping regularly in all 

 directions. Apex of the pedicle-valve scarcely prominent ; umbo 

 not conspicuous, somewhat elevated medially. Divergent cardi- 

 nal ridges, and cardinal slopes well defined. Brachial valve with 

 apex depressed and concealed ; somewhat less convex in the 

 umbonal region than the opposite valve. Surface of both valves 

 covered with a great number of fine, simple, thread-like, rarely 

 duplicating plications, of which from YO to 100 may be counted 

 on each valve near the anterior margin. 



Oriskany sandstone. Cayuga, Ontario. 



Rensselaeria ovulum. 



Plate 14, figs. 15, 16. 



Bensselceria ovulum, Hall. Palaeontology of N. Y., vol. VIII, pt. 2, expl. pi. 

 Ixxv, figs. 3, 4. 1894. 



Shell large, distinguished from B. ovoides by its more orbicular 

 form and regularly convex valves, and from B. Cayuga by its 

 larger size and greater convexity. Its outline is rather regularly 

 oval, the greatest diameter of the valves being somewhat in front 

 of the middle. Surface covered with fine radial plications. 



Oriskanv sandstone. Cayuga, Ontario. 



