NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP KAUFFMAN 3 1 



figs. 22, 23, 1869. — Meek, Macomb's Expl. Exped. from Santa Fe to Junc- 

 tion Grand and Green Rivers, p. 123, pi. 1, figs, la-d, 1876. — White, 4th 

 Ann. Rep. U. S. Geol. Surv., p. 297, pi. 41, fig. 3, 1884.— Cragin, 4th Ann. 

 Rep. Geol. Surv. Texas, p. 204 (in part), 1893. — Stanton, U. S. Geol. 

 Surv. Bull. 106, pp. 58, 59 (in part), pi. 4, figs. 1-5, non figs. 6-10, 1893 

 [1894]. — Logan, The Univ. Geol. Surv. Kansas, vol. 4, pt. 1, p. 455 (in 

 part), pi. 91, figs. 1-5, fton figs. 6-10, 1898. — Herrick and Johnson, Bull. 

 Denison Univ. Sci. Lab., vol. 40, p. 202 (in part), 1900. — Johnson, School 

 of Mines Quart., vol. 24, No. 2, pp. 186, 187, 1903a ; Columbia Univ. Contr. 

 Geol. Dept., vol. 10, No. 90, pp. 114, 115 (in part), 1903b.— Shimer and 

 Blodgett, Amer. Journ. Sci. Arts, 4th ser., vol. 25, p. 61 (in part), 1908. 



Ostrea (Alectryoma) lugiibris Conrad, Bose, Bol. Inst. Geol. Mexico, No. 30, 

 Algunas faunas del Cret. de Coahuila, pp. 47, 48, pi. 8, figs. 4-6, 1913. — 

 Shimer and Shrock, Index foss. N. Amer., p. 395, pi. 154, figs. 4, 5, 1955. 



Alectryonia lugubris (Conrad) Adkins, Handbk. Texas Cret. Foss., p. 104 

 (in part), 1928. 



DESCRIPTION 



Material. — Approximately 350 well-preserved specimens (measured) 

 and an additional 200 to 300 poorly preserved valves from various 

 localities in Texas, New Mexico, and Colorado, including most 

 illustrated types of the species. Ontogenetic series and large variation 

 suites are available from several New Mexico and Colorado localities. 



General form. — Summary of measurements presented in table 1. 

 Shell small, inequivalve, left (lower) valve slightly larger, much more 

 convex than right valve. Valves slightly to moderately inequilateral, 

 normally prosocline ; beaks, umbos typically opisthogyre (exogyroid) 

 (pi. 1, fig. 5). Left valves commonly round, subround, or broadly 

 subovate, rarely subelliptical ; right valves subovate to elliptical, slightly 

 curved (pi. 1, figs. 1-6; pi. 2, figs. 1-3, 5-12 typical of species). 

 Height normally greater than length. Anterior and ventral margins 

 slightly to moderately and unevenly rounded, posteroventral corner 

 narrowly rounded, posterior margin slightly concave to nearly straight 

 on valves with posterior auricle, otherwise moderately curved. Dorsal 

 margins short, rounded, moderately inclined anteriorly, gently sloping 

 posteriorly over auricle, recessed posteriorly adjacent to beak, umbo. 



Convexity. — Left valve moderately to highly convex, rarely flattened ; 

 high point subcentral, on ventral edge of attachment scar. Anterior, 

 posterior, ventral, ventrolateral flanks moderately to steeply sloping ; 

 dorsal and dorsolateral flanks, including attachment scar, gently 

 sloping. Right valve flat to moderately convex, normally slightly 

 arched, with umbo more inflated (pi. 2, figs. 2, 6) ; rarely concave. 

 Some right valves with upturned margins and submarginal trough. 



