40 BULLETIN OF THE LABORATORIES 



front of the middle ; concentric striae or folds appear near the front; 

 hinge plates sub-parallel, over one-seventh the length of the valves. 

 Length to width about as seven to eight. Width 24 mm, height 20 

 mm; (21-17; 18-17; 21-18; 18-15 ; 23-20.) 



Dorsal valve more nearly quadrate or sub-circular : beak short 

 and incurved ; casts showing a strong median plite within ; antero-lat- 

 eral outline se.ni-circular, postero lateral am^le very obtuse, mesial fold 

 inconspicuous, with four or five plicae, lateral areas with four to six 

 plicae. Length to width as 4-5. 



The specimens vary in many respects, but in no specimens were 

 the mesial plicae mare than four or fiv^e, there being tliree in the sinus 

 and four on the fold in normal adults. Two varieties exist side by 

 side, differing only in the number of |)lica2. 



The second agrees very closely with R. s ippho in some of its va- 

 rieties. 



This species belongs in the sandy layers or flags about 40 feet 

 below congl, I, where it is abundant. The Granville specimens are 

 said by Prof. Winchell to be typical. This is No. 13 13, of our Mu- 

 seum Register and has now for the first time been described in full. 

 Our own belief is that all of the closely allied forms belonging in this 

 section of the genus are conditions of a single species — R. sappho. 



Rhynchonella sripplio, Hall. 

 (Plate V, Fig. i; Plate VII, Fig. 25.) 



Of large size, agreeing in outline with R. sageriana, but with more 

 numerous pliccC, there being g'^nerally five in the sinus and six on 

 either side. It is possible to duplir.ite the Hamilton forms exactly 

 from our collection. 



Found in the free-stone of middle Waverly, and also in free-stones 

 from a horizon 60 feet above congl. 11, that is in the upper Waverly. 



Some of the varieties of this type resemble R. cooperensis, per- 

 fectly. 



Rliynolioiiella inarshallensis, Win. 

 This species is recognized by the ventricose, flattened dorsal valve 



