Charles B. and Mary Waux Walcott Research Fund 
LOOP DEVELOPMENT OF THE 
PENNSYLVANIAN TEREBRATULID 
CRYPTACANTHIA 
By G. ARTHUR COOPER 
Head Curator, Department of Geology 
United States National Museum 
Smithsonian Institution 
(WitH 2 PLatTEs) 
The silicified specimens forming the subject of this discussion are 
unusual in preserving parts or all of the internal skeleton in youthful 
individuals as well as adults. They were dissolved from Magdalena 
limestone taken from a ledge on the north side of an arroyo just east 
of the Grapevine Canyon road one-eighth mile south of Old Juniper 
and a cattle tank, about in the center of the W4SE4SW435 sec. 25, T. 
19 S., R. 11 E., Escondido Canyon (15’) Quadrangle, Otero County, 
N. Mex. These fossils and others described earlier from the same 
place (Cooper, 1956) are from 30 to 4o feet below the top of the 
Magdalena formation. 
The bed containing these fossils is a gray, fine-grained limestone 
containing a large amount of light-gray insoluble material and nu- 
merous other brachiopods, among which are: Cleiothyridina, Puncto- 
spirifer, Stenoscisma, Dielasma, and smaller forms still to be identified. 
Immature forms of several of the genera are very abundant and some 
small specimens appear to be adults of an undescribed genus. Gas- 
tropods and pelecypods are fairly common but their preservation is 
poor. 
One of the most abundant brachiopods in this limestone is the 
hitherto poorly known and extremely rare genus Cryptacanthia. Al- 
though this genus has been identified in many areas of Pennsylvanian 
rocks, it is one of the rarest of all Pennsylvanian fossils. The origi- 
nal specimens on which the genus was based come from Iowa but it 
is known in adjacent Illinois and Missouri. It occurs in the Gaptank 
formation in west Texas and is known elsewhere in New Mexico and 
Kansas besides the occurrences mentioned above. The genus was de- 
SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 134, NO. 3 
