74 MALONE JURASSIC FORMATION OF TEXAS. [bull. 26 I 
From all of the data above given it is seen that the shell of va 
metrica attains a much larger size than that of var. potosina, is coi 
siderably less inflated, and has a less transverse (i. e., more elevated 
and more nearly equilateral contour. 
Lucina potosina, var. metrica is not only a pronounced variety c 
its species but it is the largely preponderating representative both c 
its species and of its genus in the Upper Jurassic of western Texas. 
As is usually found to be the case where very large numbers of 
species of fossil arc available for study, L. potoshia presents cor 
siderable individual variation. Seven or eight specimens from loca 
itv \\ miles east of Malone, represent a third variety of the specie: 
which is apparently only an individual phase, though rather a striJ* 
ing one, of var. metrica. They show the following characters: Th 
shell is about as large as the largest examples of the ordinary form ti 
metrica; transversely broad-oval, inclining to subquadrate; inequi 
lateral; inflated throughout, though unequally so, the valves bein 
radially warped or flexuous, and especially swollen on the umbong 
slope, on either side of which are two broad and shallow concav 
radial zones, the anterior one of which passes downward and the pos 
terior one downward and backward; a second and smaller conve 
radial zone being developed in front of the anterior concave one. Th 
beaks are more inflated than those of the typical form of var. metricc 
The basal margin of the shell i- a little prominent and recedin, 
opposite the convex and concave zones, respectively. Corresponds, 
with the general contour of the shell, the concentric linear costella 
which in the common phase of var. metrica, have an almost unifon 
downward convexity in the posterobasal part of their course, assum 
in this phase a nearly straight or slightly upward convex trend for 
considerable distance in this part of their course, swinging upwar< 
rather suddenly anterior and posterior to it. The approximal 
dimensions are: Height, 45 mm.; length, 50 mm.: breadth, '20 mil 
This phase, then, is distinguished from the ordinary phase of vai 
'metrica by its size, average adult examples of the latter being con 
siderably smaller, by its greater and more pervasive inflation, strongl; 
flexuous valves, and more transverse and inequilateral contour. 1 
tendency toward this form is seen in some of the smaller examples o 
the other phase of metrica. 
Lucina ? emarginata sp. n. 
PI. XIII, figs i, 2. 
Cf. Cyprimeria f mexicana Castillo and Aguilera, 189f>, Bol. Coin. Geol. Mex 
No. 1, p. <>, PI. V, fig. 3. 
Shell suborbicular, compressed, though less so than that of Lncim 
potosina, var. metrica, the breadth being equal to about half of tin 
