Mr. W. H. Benson on Tany stoma tubiferum. 129 



of the interior in this species, is due, when visible, solely to 

 weathering, and is evidently not the normal state of the surface. 

 At first sight the shell might be taken for a species of Modiola, 

 and by its discoverer was supposed to be a species of Dreissena. 

 It was not until the hinge had been submitted to the lens that 

 its true characters were ascertained. 



A description of the typical species may here be subjoined in 

 an amended form. 



Scaphula Celooc, Benson. Journ. As. Soc. Calc. vol. v. p. 750 



Testa elongato-trapeziformi, albida, marginibus (superiori et inferiori) 

 parallelibus, antice rotundata, postice oblique truncata ; carina vix 

 compressa ; pagina antica, multo majori, costulis exiguis radiatis 

 munita, postica Isevi ; epidermide tenui cornea induta ; musculi 

 anterioris impressione ovata, posterioris inferiori elongato-qua- 

 drata. 



Long. 12, alt. 5, crass. 8 mill- 



Habitat in fiuminibus Jumna et Cane, necnon in rivo quodam Ben- 

 galise citra Gangem. 



In one spt^cimen, from the River Cane, the keel has a dis- 

 position to be double, with an intervening furrow. This is ap- 

 parently only an accidental variation. 



Cheltenham, 10th January 1856. 



XI. — Description of Tanystoma tubiferum, a Burmese form 

 related to tlie Genus Anostoma of Lamarck. By W. H. Ben- 

 son, Esq. 



The only Eastern shell hitherto made known which bears any 

 relation to the Brazilian genus Anostomaj is the little species dis- 

 covered by the late Capt. Boys in Rajpootana, designated by me 

 as A. Boysii. It was separated by PfeifFer under the generic 

 name of Boi/sia, and soon after by Albers as Hypostoma, A 

 singular Anostomatous shell, still more minute than Boysia, was 

 found by Mr. W. Theobald on the banks of the Irawadi. Its 

 open umbilicus, differing from the closed rim ate volution of the 

 known types, and especially the curious solute and protracted 

 last whorl and trumpet-mouthed aperture (which is dentate, as 

 in the ancient genus Anostoma), render it desirable to charac- 

 terize the shell as a new type of form, under the name of Trmy- 

 stoma, whict may be considered as generic or sectional according 

 to the views of systematists, some of whom do not admit the 

 claim of Boysia to generic separation. 



Ann. ^ Mag. N. Hist. Ser. 2. Vol xvii. 9 



