184 OKETAGEODS PERIOD. 



Surface marked by the usual lines of growth and also by numerous 

 small, flat, radiating costae of unequal Avidth, with narroAv, sharply- 

 impressed interspaces between them ; costai largest upon and near tlie 

 lunbonal ridge, becoming obsolete near the cardinal border, both anteriorly 

 and jDOsteriorly. 



Length, measuring across at about midheight of the shell, twenty- 

 eight millimeters ; height, from base to umbo, twenty -three millimeters ; 

 thickness, both valves together, about twenty millimeters. 



This species is not fully represented in the collections, but its specific 

 characters are very satisfactorily shown. A full collection of examples 

 would probably show variations of outline, due to sex, in some cases, 

 whereby the aspect of the shell may be a little different from that of the 

 figure. It is perhaps as nearly related to I. SJmmardi Meek and Hayden as 

 to any other described species, but it is clearly distinguished from that by 

 its depressed beaks and prominent umbonal ridges. 



Position and locality. — Strata of the Cretaceous period; east bank of 

 Rio Puerco, six miles below Casa Salazan, New Mexico. 



Family LUCINID^. 



Genus LUCINA Brugni{;re, 1792. 



Lucina subundata Hall and Meek. 

 Plate XVIII, fig. 12 a. 

 Lucina subundata Hall and Meek, 1856, Mem. Am. Acad. Arts & Sci., n, s., v, 382. 



Shell suborbicular in marginal outline, lenticular, moderately convex, 

 length a little greater than the height ; basal margin broadly rounded ; 

 anterior and posterior margins a little more narrowly rounded than the base; 

 postero-dorsal margin gently sloping ; beak small, slightly elevated, a trifle 

 nearer to the posterior than to the anterior side. Surface marked by the 

 ordinar}^ concentric lines of growth, which are crossed by very faint radi- 

 ating striae. 



Length, fifteen millimeters ; height, thirteen millimeters. 



Position and' locality. — Strata of the Cretaceous period ; southeast of 

 Paria, Utah. 



