28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



PS — Posterior slope of the shell, including the posterior auricle (fig. 10c). 



PVS — Posteroventral slope of the valves, bounded by the median plica, crest, 

 and posterior slope of the valve (fig. 10c). 



SC — Subcardinal cavities; shallov^ re-entrants of the valve floor beneath struc- 

 tures of the cardinal area, predominantly below the midcardinal 

 fold or lateral cardinal plates. 



SP — Secondary plica ; one that arises through bifurcation from a primary plica- 

 tion (figs. 10a, b). 



SS — Smooth stage; that portion of the beak, umbo (in many cases the whole 

 umbo), and adjacent parts of the valve that lack radiating plica- 

 tions (fig. 10b). This probably represents part or all of the 

 shell of the spat. 



T — Thickness; valve thickness is employed in this study as the actual thickness 

 of the shell material. This is naturally variable in a single valve. 

 Valve thickness should not be confused with shell or valve width. 



W — Shell width ; here defined as the broadest diameter of coattached valves when 

 viewed along the plane of the commissure. It is the length of a 

 diameter joining the high points of each valve and perpendicular 

 to the plane of symmetry. The width of a single valve is measured 

 similarly — between the high point of the valve and the com- 

 missure plane (or if the beak is overhanging, the plane passing 

 along its most projecting edge), 



SYSTEMATIC PALEONTOLOGY 

 Genus LOPHA Bolten, J. F.: Emended Kauffman, 1964 



1798. Bolten, J. F. (=Roeding, P. F.), Museum Boltenianum sive catalogus 

 cimeliorum e tribus regnis naturae, pt. 2, pp. 168, 169. 



1898. Dall, W. H., Contributions to the Tertiary Fauna of Florida. Trans. 

 Wagner Free Inst. Sci. Philadelphia, vol. 3, pt. 4, p. 672. 



1936. Maury, C. J., Brazil Servico Geol. e Mineralog., Mon. 11, p. 157. 



1937. Arkell, W. J., A monograph of British Corallian Lamellibranchia. 



Paleont. Soc, p. 180. 

 1940. Cox, L. R., The Jurassic Lamellibranch fauna of Kuchh (Cutch). Mem. 

 Geol. Surv. India, ser. 9, vol. 3, p. 95. 



Type species. — Ostrea crista-galli Linne, by subsequent designation, 

 Dall, 1898, p. 672. 



Diagnosis. — Shell normally small to moderate size, subequilateral 

 to moderately inequilateral, slightly to moderately inequivalve, left 

 valve slightly larger and more convex than right. Outline ovate, 

 subround, or subquadrate; posterior auricle commonly developed. 

 Beak opisthogyre to suberect. External ornament subequally devel- 

 oped on both valves, consisting of strong radiating plicae originating 

 at the umbone and extending to the commissure, increasing by bifurca- 

 tion and intercalation. Commissure trace undulating, more rarely zig- 

 zag. Shell structure predominantly lamellate (subnacreous layer), 



