PLATE 89, 
Page 
Fig. 1-4. Ortii is hipparionyx. 407 
1 a. A dorsal valve which retains a small portion of the shell. The direction of the striae upon 
the hinge-margin is very well shown. 
1 b. Profile view of the same. 
2 a. A similar cast, showing the vascular impressions upon the surface of the more prominent 
portions, and likewise towards the anterior margin. 
2 b. Profile of the same from the cardinal side. 
2 e. The interior of the upper part of the dorsal valve and brachial processes, as shown in a 
mould from the preceding figure. 
3. A very old specimen, in which the muscular impression is extremely elongated. 
4. The cast of a shell of medium size, preserving the muscular impression in its usual sym¬ 
metrical form. 
