MACROCHTLTNA. 39 



T. tenuicinctus, F. A. Romer, has often broader rings, i. e. only four in a space 

 equal to tlie width, but in other respects seems to agree, as far as can be judged 

 by Romer's figure. As given by Sandberger and Tschernyschew, it is so very much 

 smaller than the English fossil that it is unliJcelij to be identical. 



Affinities. — T. glaber, Trautschold,^ is very similar in shape and arrangement, 

 but the annuli are so fine that the fossil is said to have the appearance of a 

 Bacfrites or a crinoidal tentacle. 



Orthoceras, n. sp., Holzapfel," may be compared as being similar in ornament, 

 but considerably larger. 



2. Oeder— PROSOBRANCHIA, Milne-Echvards, 1848. 



There seem indications of a considerable number of univalves in the Pilton 

 beds, especially in one or two bands near the base, where some minute species 

 occur in considerable abundance. In the Mar wood zone only two species are at 

 present known to have existed. 



I. Family — Pseudomelaniid^, Fisclter, 1887. 

 1. Gemis — Macrochilina, Bayle, 1880. 

 1. Macrochilina tuebinba, n. sp. Plate V, figs. 1, 2. 



Descri])tion. — Shell small, elongate, turbinate, of three or four volutions. 

 Spire equal to half the height of the shell, convex, the upper whorls being smaller 

 in proportion than the lower. Suture simple, shallow. Whorls much exposed, 

 very broad, convex, arching out from the upper suture, flattened on the back, 

 and slightly incurving to the lower suture. Shell-structure very thin. Surface 

 smooth. 



Size. — A defective specimen is 16 mm. long and 8 mm. wide. 



Localities. — In the Barnstaple Athenaeum is a specimen from Kingdon's, 

 Shirwell, and another from Vicarage Well, Pilton. 



Remarhs. — This species, though imperfectly known, appears characterised by 

 its turbinate form, resulting from the increasingly disproportionate diminution of 

 its spire, and by its very broad whorls. The surface is shown to be smooth by a 

 small fragment of shell remaining on the figured specimen from Shirwell. 



1 1881, Trautscbold, ' Dev. Foss. Schelong,' p. 5, pi. v, fig. 5. 



2 1882, Holzapfel, ' Palseontographica,' vol. xxviii, p. 247, pi. xlvii, fig. 5. 



