Art. IX ] Herrick-Johnson, Geology of the Albttquerque Sheet. 205 
Mactra formosa, Meek. 
Plate XXXIII, Fig. 6. 
Small specimens from Carthage are referred to this species 
which is said to occur in the higher portions of the Fox Hills 
group. 
Mactra pulchella, sp. n. 
Plate XXX, Fig. 5. 
Shell small, oval-subtrigonal, compressed, somewhat longer 
than high, nearly equilateral, or with anterior side longer; basal 
margin a semi-elliptical curve, rather rapidly curving anteriorly 
and abruptly flexed to the posterior margin. Umbones ap- 
proximated, incurved ; anterior and posterior margins nearly 
straight and nearly at a right angle with each other ; posterior 
umbonal slope obscurely angular ; lunule and escutcheon well- 
marked. 
The surface is ornamented by strongly raised concentric 
plications which are relatively more conspicuous on small shells. 
Length of large specimen, 1.25 inches. In general form this 
species resembles Mactra emmonsi. Meek. The generic char- 
acters are not distinct but there is apparently an external 
ligament. 
From yellow sandstone above the Punta de la Mesa hori- 
zon, east of the Sandia mountains, near Una de Gato. 
Mactra (?) subquadrata, sp. n. 
Shell small-ovate-subquadrate, compressed, considerably 
longer than high ; anterior side much shorter ; basal outline a 
uniform semi-elliptical curve abruptly narrowed behind, broadly 
rounded in front; beaks small, approximated, distant more than 
one third the length of the shell from the anterior margin ; shell 
thin, marked by fine concentric striae. 
Length five-eighths of an inch, height one half an inch. 
The general form is much as in certain Carboniferous species of 
Edmondia. This very pretty shell occurs in the calcareous con- 
cretions of the cephalopod shales or in the “ gasteropod zone.” 
