200 PERMIAN FOSSILS. 



striated, invested with a thin epidermis. Muscular impressions round ; palhal sinus 

 strongly marked. Hinge composed of cardinal teeth, two or a single bifid tooth in one 

 valve, and one in the other ; supplementary laminae small, and often obsolete. Liga- 

 ment prominent, external." (Forbes and Hanley.^) 



PsAMMOBiA (?) SUBPAPYRACEA, King. Plate XVI, fig. 6. 



PsAMMOBiA? SUBPAPYRACEA, King. Catalogue, p. 12, 1848. 



Tellina Dunelmensis, Howse. Trans. T. N. F. C, vol. i, p. 243, 1848. 



Diagnosis. — " A thin, smooth, elliptical species. Length one third of its width : 

 umbones slightly prominent, one third of the width of the valves from the anterior end : 

 terminations rounded.'' (King.^) 



The fossil under consideration, which rarely exceeds an inch in width, is pro- 

 visionally placed in the present genus ; as nothing certain is yet known respecting its 

 dental and muscular characters. Judging from its outline, — some slight indications of 

 cardinal teeth, — and, the absence of the posterior flexure, which certain Psammobiida 

 possess, notably Tellina, the present genus seems to be its most appropriate receptacle. 



Psammobia (?) subpapgracea occurs very rarely in the Shell-limestone of Humbleton 

 Hill. 



Class Gasteropoda, Cuvier. 



MoNOTHYEA, Aristotle. 

 Teachelipoda, &c., Lamarck. 

 PAEAcipHALOEES, BlainvUle. 

 Les Apt^eygiens, &c., Latreille. 

 Uniloculaiees {partim), Be Montfort. 

 Univalves. 



Diagnosis. — " Body free : with an abdominal foot suitable for creeping, and in some 

 cases for swimming. Head in general distinct, usually bearing one or more pairs of 

 tentacles. Dges situated nearly always on or near the tentacles.^ Bespiratorg organs 

 branchial or pulmonary, and very variable in their position. Shell either external or 



^ British MoUusca, vol. i, p. 270. Feeling averse to overlooking the original diagnosis of a genus or 

 species, I transcribe the following description of Psammobia by its founder : " Testa transversa, elliptica 

 aut ovato-oblonga, planiuscula, utroque latere paulisper hians ; natibus prominuhs, Cardo dentibus 

 duobus in vaM sinistra ; dente unico inserto in opposite." (Animaux sans Vert^bres, 2d ed., t. vi, 

 pp. 170-1.) 



2 Catalogue, p. 12. 



^ ChitonidcB possesses no eyes. 



