A NEW FOSSIL SPONGE FROM THE ORDOVICIAN GARDEN CITY LIMESTONE OF SOUTHEASTERN IDAHO J. Keith Rigby' and James K. Gilland' Abstract.— The new choristid demosponge, Loganiella johnsoni, is described from the upper part of the Lower Ordovician Garden City Formation of southeastern Idaho. The new sponge is a relatively thin walled, low, sub-cylindrical form. The skeletal net is composed of tracts of curved rodlike spicules, but details have been lost on all specimens because of extensive silicification. Impressions, however, suggest a close relationship to the choristid Dystactospongia Miller, 1889. Several specimens of a new sponge were collected from the Ordovician Garden City Limestone by Victor Church during a study of the Preston Quadrangle in southeastern Idaho in 194 L He was assisted by Chester O. Johnson of Gustavus Adolphus College during the study. Dr. Johnson kindly loaned us the collection of sponges he made at that time. A collection of sponges was also given to Utah State University by Mr. Church. These sponges were loaned to us by Dr. J. Stewart Williams and incorporated in this study. The Garden City Formation was named for exposures in the Bear Lake region of northern Utah and southeastern Idaho by G. B. Richardson (19L3: 407-408, 1914: 13-16) and includes the Lower Ordovician beds be-tween the underlying Cambrian St. Charles Limestone and the overlying Swan Peak Quartzite. The formation is approximately 900 feet thick in the type section, which is approximately 15 miles east of the locality where the sponges were collected. The Garden City Limestone was later restudied in detail by R. J. Ross, Jr. (1949, 1951). He described the fauna and zoned the formation utilizing the moderately abundant trilobites and other fossils and es-tablished an alphabetic zonation, parallel to that utilized by Hintze (1951, 1952) for equivalent beds of the Pogonip Group in western Utah and eastern Nevada. The fossils were collected from E V2, NW 1/4, SE 1/4 Section 30, Township 16 South, Range 42 East, in southern Franklin Coun-ty, southern Idaho (Map 1). The locality is along the west face of Crab Ridge near the ridge crest, .2 mi. north of the Utah-Idaho boundary. Crab Ridge is a prominent linear feature along the east side of the head-waters of Logan River. Johnson (1962, pers. comm.) notes that there are no major outcrops in the wooded slope along the east side of Logan River valley near where the sponges were collect-ed from talus fragments. There seems little question, however, that the material came from near the crest of Crab Ridge because of the location of the talus on the slope. The sponges are silicified and some of the better specimens were etched free of matrix by dissolving the limestone in dilute acetic acid. Many small, spherical, HindiaAike sponges(?) were recovered in the residue, along with numerous conodonts. The con-odonts were sent to Dr. Raymond L. Eth-ington of the Department of Geology, Uni-versity of Missouri for identification and zonation. Ethington and Clark (Hintze 1977) have established a conodont zonation for the Pogonip Group in western Utah and eastern Nevada and have tied this to the trilobite zones of Hintze and Ross (1950). On the basis of the conodonts the sponges came from rocks of zone J to L (Ethington, 1977, pers. comm.). Conodonts recovered from the matrix around the holotype (BYU 1090) include the following forms, identified by Ethington: Department of Geology, Brigham Young University, Provo, Utah 84602. 475
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