596 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
the genus Perimeococoelia rather than Parastrophina and are referred to P. semi- 
costata. The Minnesota species Parastrophina rotundiformis is a much larger 
one with more convex valves than the Virginia species. Furthermore, the Prosser 
form is more strongly costate and the costae extend at least to the middle of the 
valves. 
PERIMECOCOELIA TRIANGULATA Cooper, new species 
Plate 117, B, figures 3-12 
Shell small for the genus, triangular in outline; greatest width anterior to the 
middle ; anterolateral extremities narrowly rounded; sides slightly convex. Pos- 
terior two-thirds smooth, anterior third costate, 2 costae marking the sulcus, 
3 the fold, and 1 strong costa and an obscure one marking the flanks. 
Pedicle valve gently convex in the posterior half, nearly flat anteriorly ; um- 
bonal region gently swollen; sulcus originating anterior to the middle, moder- 
ately deep and forming a short, truncated tongue anteriorly; flanks narrow, 
slightly deflected in the direction of the pedicle valve toward the front. 
Brachial valve 2 to 3 times as deep as the pedicle valve, moderately convex 
in lateral profile with strongly arched and swollen umbo that protrudes anterior 
to the pedicle beak. Fold originating near the middle, narrow, low; flanks de- 
pressed, strongly rounded and with steep slopes to the margins. 
Measurements in mm.—Holotype, length 7.8, brachial length 7.9, width 8.2, 
thickness 6.4. 
Types.—Holotype: 111342a; unfigured paratypes: 111342b-f. 
Horizon and locality—Effna formation in Virginia: Porterfield Quarry, 5 
miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Discussion.—This species differs markedly from P. semicostata in outline and 
proportions although the costation is similar. 
PLECTOCAMARA Cooper, new genus 
(Greek plektos, fold; camara, chamber) 
Shells small to moderately large, rhynchonelloid in outline and profile. Pedicle 
valve shallower than the brachial valve and with a deep sulcus and long tongue. 
Beak suberect ; delthyrium as in all camerellids. Brachial valve with prominent 
median fold. Valves completely costate ; entire surface covered by closely crowded 
wavy, elevated, concentric lines. Pedicle interior with deep, narrow spondylium 
supported by a short median septum. Brachial interior with short brachiophores 
attached to the floor of the valve to form a narrow notothyrial cavity. Median 
septum absent or only a short ridge in front of the notothyrial cavity. 
Genotype.—Plectocamara costata Cooper, new species. 
Discussion—At first glance the species of this genus suggest small rhyncho- 
nellids such as Camarotoechia or Rhynchotrema, but study of the delthyrial re- 
gion, which has no deltidial plates and is like Camerella, will, along with the 
interiors, help to distinguish these peculiar little shells. Inside the pedicle valve 
the spondylium is long, narrow, and deep and is sessile at the posterior as is 
