750 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
rapidly to cardinal extremities. Umbonal region only slightly concave; region on 
each side of umbo and along posterior margin flattened. Interarea short, about 
half the length of the pedicle interarea ; hypercline. 
Interior: Pedicle valve having dental plates strong with deep umbonal cavi- 
ties, sloping inward; teeth small; delthyrial chamber deep. Muscle field thick- 
ened, short as usual in the genus. Ridge in front of muscle field extending to 
about middle. Brachial valve with long, slender brachial processes extending 
strongly anterolaterally. Other visible features as usual in the genus. 
Measurements in mm.— 
Brachial Surface Mid- Hinge Thick- 
Length length length width width ness Height 
Eolotyge v.20 RA, 6.9 5.8 9.0 8.5 9.7 1.9 3.3 
Hypotype (71499a)... 7.8 6.4 9.5 8.7 8.9 2.1 37 
“~ (117436d).. 10.2 7.5 13.5 10.8 110+ 2.9 5.0 
« (117436a).. 8.4 6.9 11.5 8.8 10.7 2.4 4.6 
Types——Holotype: 71500; figured hypotypes: 117436a,d,e; unfigured hypo- 
types: 71499a, 117436b,c. 
Horizon and locality.—Little Oak formation in Alabama: 4 mile north-north- 
east of Pelham, Bessemer Iron District (15’) Quadrangle; west side U. S. High- 
way 31, SWiSW43 sec. 13, T. 20 S., R. 3 W., 4 mile N. 10° E. of Pelham Sta- 
tion, 2 miles north of Pelham, Bessemer Iron District (15’) Quadrangle; inter- 
section of Bailey Gap road with main road, SW4SW43 sec. 13, T. 19 S., R 2 W., 
13 miles northeast of Newhope Church, Vandiver (15’) Quadrangle. 
Discussion—This species is somewhat variable and has an interesting growth 
development. The young are transverse and have acute cardinal extremities. The 
adult form has an unusually long interarea on the pedicle valve, and the outline 
becomes strongly rectangular with the length slightly less than the width. The 
long interarea on the pedicle valve, the deep brachial valve and rectangular form 
distinguish L. delicatula from all the other species herein described. This species 
never attains the large size of L. tennesseensis which is its closest relative in time 
and appearance. 
LEPTELLINA INCOMPTA Cooper, new species 
Plate 191, B, figures 9-22 
Shell of about medium size for the genus, wider than long with the hinge equal 
to or forming the greatest width; sides moderately oblique, gently rounded; an- 
terior broadly rounded ; costellae not visible on perfect specimens because of the 
crowded, thin lamellae which give the shell a rough or untrimmed appearance ; 
costellae of 2 sizes, the larger ones about I mm. apart at the front margin of an 
adult, remainder of shell covered by a mat of fine costellae. 
Pedicle valve evenly and moderately convex in lateral profile; anterior profile 
moderately domed, with the median region somewhat narrowly convex and with 
long, steep lateral slopes. Beak small and narrowly protruding slightly posterior 
to the posterior margin; umbo moderately convex; median region moderately 
swollen; posterior slope shorter and somewhat steeper than the anterior slope. 
