PLATE 107. 
Page 
'ig. 1 - 15. Rensselaiiua suessana. 459 
1. Dorsal view of a specimen of a symmetrically oval form. 
2. A specimen showing a more prominent beak and contracted front. 
3 a, b. Ventral and dorsal views of a specimen of less extreme form than the preceding. 
4. An elongate form which is more symmetrically oval. 
5 a. Dorsal view of a small specimen of the prevailing or characteristic form. 
5 b. Profile view of the preceding, showing a scarcely perceptible incurving of the valves at 
their lateral margins. 
5 c. Dorsal view of an older specimen, showing the perfect condition of the shell. 
5 d. Profile view of the same, showing the inflected margins of the shell. 
5 c, f, g h h. Dorsal, ventral, and profile views of a full-grown specimen of this species. 
6. A cast of a similar form. 
7. The interior of two ventral valves, one preserving the deltidial plates and the other without 
them. The muscular impressions are but feebly preserved. 
8. The interior of two dorsal valves; the one showing the hinge-plates in their usual form, 
and the upper one having them much thickened : in the latter, the crura diverge at their 
origin, while in the other they proceed in a longitudinal direction for a short distance 
before bifurcating. 
9. The dorsal valve, showing the hinge-plates, dental fossets, foramen, crura and crural plate, 
and appendages. The figure is slightly enlarged. 
10. The figure of a similar specimen, where the hinge-plates are much thickened and rounded, 
the crura branching near the base, and the crural plate narrower than in the preceding. 
11. A diagram showing a longitudinal section of the two valves in connexion, with the crura 
and appendages. 
12. 13, 14 & 15. Figures showing the variety of form of the crural plate, as observed in several 
individuals of this species. 
