NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 27 



H : HSS — The ratio of the valve height to the height of the smooth stage on 

 the early portion of the valve. 



i — The angle of inclination of the valve (fig. 10c) ; the angle between the 

 plane of the hinge line (horizontal) and a line connecting the 

 beak (or center of the attachment scar) with the most distant 

 edge of the shell. This line generally roughly bisects the shell. 



ICL — Imbricating concentric lamellae; the major concentric features of the 

 ornamentation (fig. 10b). 



IPS — Interplical sulcus; the trough between any two plicae. The auricular sulci 

 are enlarged interplical sulci separating the auricles from the 

 main body of the shell (figs. 10a, b). 



LCP — Lateral cardinal plates (fig. lOd, 5a-c) ; triangular flat areas for liga- 

 ment attachment on either side of the resilifer and midcardinal 

 fold (right valve). These are highly variable in size, and com- 

 monly bordered laterally by a shallow groove (marginal cardinal 

 trough). 



L :LHL — Ratio of the length of the valve to the length of the hinge line. 



L : LPA — Ratio of the length of the valve to the length of the posterior auricle. 



MCT — Marginal cardinal trough. A shallow, narrow groove or trough on the 

 cardinal area between the lateral cardinal plate and upturned 

 lateral margin of the valve (fig. lOd). 



MF — Midcardinal fold. The raised convex portion of the central cardinal area 

 on the right (upper) valve, below the resilifer (where present). 

 It occupies from one-fourth to the whole of the area. 



ML — Microlamellae ; very fine overlapping sheets of lamellar calcite. The 

 major ornament on the smooth stage of the shell and between 

 imbricating concentric lamellae over the rest of the shell (fig. 

 lOb). They appear as simple growth lines in many cases. 



MP — Median plica (figs. 10a, c) ; the major primary plication that runs down 

 the approximate center of the valve, passing through its high 

 point. It is usually the most prominent plica on the shell, and is 

 a useful reference line for defining the various flanks. 



MSD — Maximum scar diameter (fig. lOd) ; the longest diameter of the posterior 

 adductor muscle scar, the least variable parameter of the scar 

 to measure ; useful in ontogenetic study. 



PA — Posterior auricle (figs. lOa-c), or wing of the shell (in the sense of 

 Newell, 1942, p. 22 as applied to the Mytilacea). This is a 

 prominent, flattened, projecting salient of the posterior and 

 dorsoposterior flanks of the shell, in some cases separated from 

 the main body of the shell by an auricular sulcus. 



paa — Posterior auricular angle (fig. 10c) ; the angle between the dorsoposterior 

 margin of the posterior auricle and the plane of the hinge line 

 (horizontal reference line). 



PD — Plication density. The number of plications per unit approximate shell 

 area (HXL). 



PLS — Posteroventral lip of the adductor muscle scar (fig. lOd). A raised ridge 

 that bounds the scar posteriorly and ventrally in many species. 



PP — Primary plica ; one of the initial plications of the shell, arising at the edge 

 of the smooth stage and extending to the shell margin. It may or 

 may not give rise to other plicae by bifurcation (fig. 10a, b). 



