860 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
the brachiophore. Cardinal process bipartite; shafts short, stout, attached to 
floor of valve; myophores with 2 or more ridges. 
Interior of brachial valve divided into unequal parts, a posterior portion oc- 
cupying about one-third the length and an anterior portion occupying the re- 
mainder. Posterior third including the adductor field usually bent at an angle 
to the anterior portion which probably carried the lophophore. In front of the 
shafts of the cardinal process 2 ridges originate and extend anteriorly, rising to 
a crest at the point of geniculation between the anterior and posterior portions 
of the valve. From the point of geniculation these ridges extend almost to the 
margin, then curve laterally by a narrow loop and swing posteriorly. At the 
geniculation they again rise to a crest and extend posteriorly to end under the 
brachiophores. These ridges are strongly elevated where they bound the adduc- 
tor field. At the line of geniculation more or less prominent callosities are de- 
veloped in front of the anterior adductor impressions. In some specimens these 
callosities may be produced into projecting processes. The adductor scars are 
obliquely placed, the anterior pair lying in the anteromedian corner of the field 
and the other pair outside in the posterolateral corner. 
Genotype—Laptaena subquadrata Hall, 2d Ann. Rep., New York State 
Geol., pl. 46, figs. 32, 33, 1883. 
Discussion.—This genus has not lately been subjected to a careful study. The 
result is that a number of species have been placed in it that do not belong. 
Christiania lamellosa Bassler from the Oranda formation of Virginia and Penn- 
sylvania and C. youngiana (Davidson) from the Stinchar limestone of the Girvan 
District, Scotland, must be excluded. These two species have been removed to 
the genus Bimuria Ulrich and Cooper. 
CHRISTIANIA AURICULATA Cooper, new species 
Plate 215, D, figure 13; plate 215, F, figures 20-28 
Christiania trentonensis brevis Butts, Virginia Geol. Surv. Bull. 52, pt. 2, p. 109, pl. 95, 
figs. 2, 3 (not 1 = Bimuria lamellosa), 1942. 
C. cf. C. trentonensis Butts (not Ruedemann), idem, figs. 4-6. 
Shell of about usual size for the genus, longer than wide; elongate, subrec- 
tangular in outline with the sides usually somewhat concave inward or sub- 
parallel. Anterior margin narrowly rounded to subnasute; hinge usually as 
wide as or slightly wider than the midwidth. Cardinal extremities moderately 
auriculate. Surface marked by more or less regular concentric growth lines. 
Pedicle valve strongly convex in lateral profile with the maximum curvature 
located at the umbo; anterior profile narrowly convex and with precipitous sides. 
Umbo strongly swollen and protruding posterior to the posterior margin ; median 
region strongly but narrowly swollen; sides nearly vertical; interarea long; 
anacline. Pseudodeltidium short, wide, and strongly convex. 
Brachial valve narrowly and deeply concave, most concave near the middle; 
sides and anterior margins strongly bent toward the brachial direction ; interior 
with strong ridges; adductor field bordered anteriorly by a strong, transverse 
ridge. Cardinal process moderately large. 
