2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
scribed by White and St. John (1867) but little has been written 
about it since then. Dunbar and Condra (1932) redescribed the 
genus and added another species from the early Permian. Study of 
the specimens described herein and of another preparation of the loop 
of Cryptacanthia from Madison County, Iowa, shows that this struc- 
ture was improperly restored by Dunbar and Condra. 
About a dozen blocks of various sizes were collected at the locality 
in Grapevine Canyon. These yielded about 4,000 specimens of 
Cryptacanthia, including many with almost perfect interiors and some 
with the loop preserved to perfection. These specimens permit a 
nearly complete description of the development of the loop and other 
details of the interior. This is the first Paleozoic long-looped brachio- 
pod in which the stages of loop development have been described. 
In comparing the New Mexico specimens with those from Iowa, 
which are topotypes, it was discovered that the ones from the South- 
west are clearly a new species for which the name Cryptacanthia pro- 
lifica Cooper is here proposed. 
CRYPTACANTHIA PROLIFICA Cooper, new species 
Small, pentagonal in outline, length and width nearly equal but 
varying from an oval outline in the young to subpentagonal in the 
adult ; inequivalve, the pedicle valve having the greater depth, postero- 
lateral margins nearly straight forming an angle at the beak of 105° 
to 110°; sides narrowly rounded; anterolateral margins gently con- 
cave to straight; anterior margin truncated to gently emarginate; 
greatest width at about midvalve but variable with age; anterior com- 
missure strongly sulcate; surface smooth. 
Pedicle valve evenly and strongly convex, with the maximum con- 
vexity at the middle ; anterior profile narrowly domed with steep, con- 
cave sides ; beak small, incurved, suberect to erect ; foramen elongate- 
elliptical, mesothyrid to submesothyrid; deltidial plates conjunct; 
umbo narrow, moderately convex; fold originating on anterior side 
of umbo, widening anteriorly to front margin, somewhat flat-topped 
and with a sulcus originating at about midvalve; umbonal slopes 
gentle, anterolateral slopes precipitate. 
Brachial valve shallow, evenly and gently convex in lateral profile; 
anterior profile nearly flat but with a shallow median depression ; 
umbo gently swollen; sulcus originating just anterior to the umbo, 
widening and deepening anteriorly to the front margin; sulcus in 
many specimens with a low, indistinct fold originating just anterior to 
