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OpiEEOULA OP Gasteropoda. 

 Plate 3, flgs. 10, 10a, 10b, and 11, and pi. 7, fig. 7. 



Sevei-al specimens of the operculum or opercula of one or more 

 species of holostomatous gasteropoda have been collected at Hespeler 

 by Ml-. T. C. Weston and at Durham by Mi-. J. Townsend, the 

 largest of which measures fully three quarters of an inch in its greatest 

 diameter. These opercula are all calcai-eous, thick, circular in outline 

 and multispii-al. Though often perfect and well preserved, the 

 sculpture of their outer surface is usually obscured and nearly covered 

 by small portions of the tenacious matrix. So far they have never 

 been found in place, so that it is quite uncertain to which species they 

 belong or to how many. 



In certain specimens (such as the one represented by figures 10, 10a 

 and 10b of plate 3, which for convenience may be called ISTo. 1) 

 the outer side is conical and moderately elevated, — the height of the 

 cone being usually rather less than one-half the diameter of its base, — 

 the apex is subcentral, the whorls are sinistral and bounded externally 

 with a thin, laminar, raised ridge, the spaces between the coils of which 

 are obliquely striated across. On their inner sides (which, however, 

 are possibly imperfect) they are gently concave, the central portion 

 paucispiral and the outer obscurely animlar. 



In other individuals (such as the original of figure 11 on plate 3, 

 which may be distinguished temporarily as operculum No. 2,) the 

 outer side is much more compressed than that of No. 1, and might 

 better be described as depressed convex rather than conical. The inner 

 surface of No. 2 is neai-ly flat and marked with concentric annular 

 striations, but there is a small pit in the centre, and a rather narrow, 

 elevated and annular rim around its outer margin. 



It is most probable that these opercula belong to shells of the genus 

 Euomphahis or Straparollus, in the sense at least in which these words 

 are used in this article, perhaps to ' E. Galtensis or S. crenulatus. 

 Stoliczka says* that the opercula of Euomphalus (which he regards as a 

 synonym of Straparollus) " very much resemble those of Torinia, being 

 thick and composed of numerous lamellar volutions/' a description 

 which would apply perfectly to those from Durham. On the other 

 hand, the opercula of Euomphalus funatus, as figured by Baileyf are 

 also very like the Durham specimens, and this similarity would rather 

 favour the view that the latter may be the opercula of Straparollut 

 crenulatus. 



* Paleontologia Indica. Cretaceous Fauna of Southern India, page 254. 



t Figures of Characteristic British Fossils, vol. 1, plate 21, fig. 9. 



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