72 MALONP: JURASSIC FORMATION OF TEXAS. [bull. 2G6. 
LITCINID^]. 
Genus LUCINA Brug. 
Llcima potosina C. and A. 
PL XIII, figs. 4, 5. 
Lucina potosina Castillo and Aguilera, 1895, Bol. Com. Geol. Mex., No. 1. 
p. 6, PL IV. figs. 2, ,°>, and 6; and PL V, figs. 11 to 14. 
Five specimens from the locality H miles east of Malone station 
seem to agree sufficiently well in size and form with the small, trans- 
verse and rather inflated Sierra de Catorce shells that constitute the 
type variety of Lucina potosina. 
The following is a translation of Castillo and Aguilera's descrip- 
tion of the species: 
Shell transversely oval, relatively compressed, inequilateral. Buccal region 
longer than the anal, uniformly rounded at its extremity and nearly of the same 
width as the anal. Lunnle well developed, rather deep and generally wider in 
the right valve. Anal region nearly of the same breadth as the buccal, rounded 
at its extremity, more inflated than the buccal region. Ligamental area narrow, 
dec]), and elongated, occupying the whole length of the anal region. Cardinal 
border slightly concave on the buccal side and straight or gently convex on the 
anal side. Inihones snhcentral, contiguous, and a little inclined to the hnccal 
side. Ventral or lower border little curved, joined to the anterior and posterioi 
borders by arcs of more pronounced curve than its general curvature. Flanks 
convex, more inflated below the beaks where the major convexity is found; this 
diminishes gradually toward the borders. Surface adorned with delicate con* 
centric eostellse, little salient and separated by plain intervals four to six times 
wider than the costelhc Length, 1!>, 20.5, 21 mm.; breadth, in relation to tilt j 
length. 0.79, 0.80, 0.85; thickness, in relation to the length, 0.47, 0.48, 0.48. 
The exact geological position of Lucina potosina at its type localitj 
is not known, as the records are somewhat conflicting. Castillo anj 
Aguilera state, on page 8 of the above-cited bulletin, that the types 
of this species and of Cyprina coteroi were found associated witl 
Alamitos fossils, but were petrified in flint, believed to have been de 
rived from the flint -bearing limestones of their " grupo superior," tha 
overlie the sandstones of the Cieneguita (Lower Cretaceous) as tin 
Cieneguita in turn overlies the Alamitos (Upper Jurassic). On pag< 
-19 of the same they omit Cyprina coteroi, but include Lucina potosim 
in the list of fossils of the grupo superior, and state that Schloenbachn 
af. inflata is the only fossil found in the limestones of the grup< 
superior, ascribing Lucina potosina and the other fossils of the grujj 
superior to calcareous and marly shale below the limestone, in t\v 
base of the grupo. Finally, on page 50, Cyprina coteroi is given a 
one of the fossils of the Alamitos beds, which are Upper Jurassic 
In view of the confusion that has arisen regarding the original strati 
graphic source of these fossils, and the further fact that the actul 
collecting of them seems to have been from among the fossils of th 
Alamitos, there would appear to be some uncertainty as to thei 
