LOWER CAMBRIAN HALKIERIIDS AND OTHER COELOSCLERITOPHORANS FROM AKSU-WUSHI, XINJIANG, CHINA

Halkieriids are known largely from isolated sclerites, although it is understood that originally they formed the scleritomes of slug-like an imals in Lower Cambrian benthic environments. The Yurtus Formation (?T ommotian-Atdabanian equivalent) of the Aksu-Wushi area, west Xinjiang, China, has yielded abundant sclerites. These are secondarily phosphat ized, but show considerable detail. The sclerites can be divided into three classes: cultrates, long palmates, and short palmates; definite siculates have not been recognized. In some samples elongate to semici rcular shells co-occur with the sclerites; these may derive from the s ame halkieriid scleritome. The external surface of the shells may bear a subdued ornamentation. The concave interior, however, is remarkable on account of a unique structure consisting of a group of nodular-lik e units. These may be arranged in a low cone or dispersed in a small c ircle. In addition to the sclerites of halkieriids and their possibly associated shells, rarer material is attributable to the related group of siphogonuchitids.