1 88 



NEW YORK STATE MUSEUM 



Genus rhipidomella Oehlert 



[Ety. : finis, fan] 



(1891. Journal de conchyliologic, p. 372; 1892. Pal. N. Y. v. 8^ 

 pt 1, p. 209) 



Shell almost circular in outline; both valves gently convex; hinge- 

 area short; slight median depression in each valve. Surface cov- 

 ered with fine, rounded, hollow, tubular striae, which frequently open 

 on the surface. On the interior of the pedicle valve are two strong 

 diverging teeth. Muscular area large, and deeply impressed, con- 

 sisting of fluted diductor impressions, inclosing small central ad- 

 ductors. The pedicle scar fills the cavity of the beak. The interior 

 of the brachial valve shows deep and narrow dental sockets, with 

 prominent projecting crural plates. In the center is a strong car- 

 dinal process, below which is the indistinct small muscular area. 



Rhipidomella hybrida (Sowerby) (Fig. 98). O r t h i s h y - 

 brida Sowerby (Hall. 1852. Pal. N. Y. 2:253, pi. 52) 



Distinguishing characters. Wider 

 than long; nearly equal valves; pedi- 

 cle valve with broad, undefined de- 

 pression down the center; brachial 

 valve uniformly convex, sometimes- 

 slightly depressed near front; beaks 

 nearly equally elevated and scarcely 

 incurved; short hinge area; fine bi- 

 furcating striae. 



Found in the upper part of the lower Rochester shales and in the 

 Bryozoa bed as well as rarely in the upper shales. Niagara sec- 

 tions. Also at Lockport and elsewhere (Hall). 



Rhipidomella circulus Hall (Fig. 99). O r t h i s circulus 

 Hall (1852. Pal. N. Y. 2:56, pi. 20) 



Fig. 98 Rhipidomella hybrida 



Fig. 99 Rhipidomella circulus with enlargement of surface 



