a1 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
Ninella tarimensis from the Lower Cambrian Yurtus Formation of western Xinjiang, China, is shown to be a relative of the halkieriids and siphogonuchitids. These are known principally from dispersed sclerites, presumably secreted by slug-like organisms that were an abundant component of the Cambrian benthos. The sclerites of N. tarimensis are relatively small, strongly recurved and usually possess an upper surface ornamented with transverse sculpture. The lower surface is more or less smooth and is joined to the upper surface via steep faces that may be grooved. The apertural region is quadrate in outline and bears a circular foramen. Ninella is fairly widespread and is known from elsewhere in China (Guizhou and Shaanxi Provinces) and from Kazakhstan. A brief description of the siphogonuchitid scleritome is also presented, based on dispersed sclerites and shells from the Lower Cambrian of Shaanxi Province, China. Formal synonymy of the sciotaxa Siphogonuchites, Dabashanites, Lopochites, and Maikhanella as Siphogonuchites is proposed.
(Received July 13 1995)
(Accepted September 14 1995)