NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 



39 



relatively more convex right valves, relatively larger muscle scar, a 

 less inflated midcardinal fold (where present), and in having the 

 resilifer relatively larger than either lateral cardinal plate or fold. 

 It may be further distinguished from older species by the external 

 ornamentation of the valves. In L. luguhris, the majority of right 

 valves lack plicae, and smooth left valves are common. Plicate 

 valves may be distinguished from those of older species in the follow- 



30 



25 



2 

 S20 



il5 

 u 



^lO 



< 

 > 



5 10 15 



LENGTH: BEAK TO 



POSTERIOR EDGE 



(MM) 



VALVE HEIGHT (MM) 



VALVE HEIGHT (MM) 



Fig. 12. — Ontogeny in Lopha lugtibris (Conrad). A, Relationship between 

 length of the left valve and the distance between the beak and posterior edge, 

 measured parallel to the length. B, C, Relationship between height and length 

 of the left and right valves, respectively. Approximate boundaries between 

 ontogenetic stages marked by dashed lines. N = Neanic ; E := Ephebic ; 

 G =: Gerontic. 



ing manner : The plicae appear at a later stage of development, rarely 

 bifurcate, and then only in the ephebic stage, and are smaller, nar- 

 rower, and more numerous than those of other species. The auricular 

 plicae are similar to those of the main body of the shell. L. lugubris is 

 further distinct in generally lacking coarse concentric sculpture, and 

 in having the plicae well defined on part of the valve interior. 



No species of oysters known to me are closely comparable to L. 

 luguhris, although marginal variants of some North American and 

 foreign species resemble it. Notable among these are "Ostrea" semi- 

 plana Sowerby, L. bellaplicata hellaplicata, and L. panda Morton. 



No consistent ecologic control on any morphologic feature was 



