A LATE PERMIAN CHINESE GASTROPOD SPECIES, POSSIBLY LARVAL, IN THE MIDDLE PENNSYLVANIAN OF NEW MEXICO

Abstract

Kues and Batten (2001, p. 30, fig. 6.17–6.20) described several distinctive, minute, low-spired gastropod specimens from the Desmoinesian (Middle Pennsylvanian) Flechado Formation of northcentral New Mexico, assigning them questionably to Lunulazona Sadlick and Nielsen, 1963 because of the strongly developed collabral elements similar to those of that genus. These shells, consisting of three or four inflated whorls, are at most 1 mm in height and the later whorls bear conspicuous, sharp, widely spaced collabral ribs that bend strongly across a wide, slightly flattened band interpreted as a peripheral selenizone. While recognizing these specimens as a distinct, unnamed taxon, Kues and Batten (2001) believed that they likely represent juveniles of an as yet unrecognized larger species of gastropod with a different mature morphology. Recently, Pan and Erwin (2002) described diverse gastropod assemblages from southern China, most of them from Late Permian (Changhsingian) strata. Most of these taxa are very small, possibly reflecting differential silicification rather than adverse or unusual ecological conditions. Among the specimens is a single, beautifully preserved shell, described as Naticasinus sinus new genus and species (p. 6, fig. 4.14–4.16), from the upper member of the Heshan Formation, of very late Permian age. This specimen is similar in size, whorl proportions, and number of whorls to the New Mexico Middle Pennsylvanian specimens, and furthermore possesses nearly identical ornamentation. Pan and Erwin interpreted a sinus and lunulae just below midheight, but lacking the parallel sides that would indicate the presence of a slit. The shell characters of the New Mexico Middle Pennsylvanian specimens are so closely similar to those of the Chinese species that, on purely morphological grounds, they would appear to represent an early occurrence of Naticasinus sinus n. gen. and sp. The similarity between Lunulazona ? sp. and Naticasinus sinus n. gen. and sp. was noted by Bandel …