1922.] B. Prashad: Burmese Unionidae 109 



An examination of the types of Unio giannelli , its var. degener, 

 L. marginal is var. sublamellata and shells identified as var. zonata > 

 has shown that they are all referrable to this species. The shells 

 of var. humilior von Martens also gradually fade into those of the 

 typical form and it is impossible, therefore, to distinguish this 

 variety. 



L. scutum has a comparatively less broad, less tumid, but 

 more elongate type of shell than that of either L. generosus or 

 L. lamellalus — the other two species of this interesting group. 

 The group, so far as is known at present, is confined to Burma. 



Genus Trapezoidcus Simpson. 



1921. Trapezoid 'ens, Pra<;had, Fee. hid. Mns. XXII, p. 609. 

 In the paper cited above I have described the anatomy of 

 this interesting genus. In Burma it. is represented by five species, 

 all of which, with the exception of T. foliaceus, are endemic in 

 Burma. 



Trapezoidcus cxolescens (Gould). 



184,3. Unio exolescens, Gould, op. cit., p. 141. 

 1852. Margaron (Unio) exolescens, l.ca, Synoyms, p. 32. 

 1862. Unio exolescens, Gould, Oiia Conch., p. 191. 



1866. Unio exolescens, Blanford, Journ. As. Soc. Bengal, XXXV, pt. 

 i, p. '49- 



1876. Unio exolescens, Hanley and Theobald, op. cit., p. 43, pi. cvii, 



%• 5- 



1877. Unto fragilis, Nevill, Journ. As. Soc. Bengal, XLVl, p. 39. 



1878. Unio foliaceus var. fragilis, Nevill, op. cit., p. 400, pi. lxxx, 



fig. 8. 

 1889. Unto exolescens, Iapparone-Canefri, op, cit., p. 349. 



1899. Unio exolescens, von Martens, op. cit., p. 42. 



1900. Trapezoideus exolescens, Simpson, op. cit., p. 859. 



1914. Trapezoideus exolescens, Simpson, op. cit., p. 1185. 



1915. Trapezoideus exolescens, Preston, op. cit , p. 195. 

 1920. Trapezoideus exolescens, Haas, op. cit., p. 272. 



An examination of Nevill 's type of Unio fragilis has shown 

 that the species should be referred to T. exolescens rather than to 

 var. comptus of T. foliaceus as. Simpson thought (loc. cit. } p. 1182) 

 or to T. misellus as Haas has done. One of the specimens in 

 Fea's collection is labelled ' Unio microsomus , T. Canefri, n. sp./ but 

 this is not referred to in his paper; the specimen is only a young 

 example of T. exolescens ; the other shells referred by T. Canefri to 

 T. exolescens are correctly identified. 



The locality of the type-specimens was not certain, but von 

 Martens' specimens were obtained at Mandalay and the Indian 

 Museum specimens are from Bhamo. 



Trapezoidcus foliaceus (Gould). 



1843. Unio foliacea, Gould, op. cit., p. 141. 

 1852. Margaron (Unio') foliacea, Lea, op. cit., p. 39. 

 1862. Unio foliacea, Gould, op. cit., p. 191. 



1865. Unio Peguensis, Anthony, A tner. Journ. Conch. I, p. 351, pi 

 xxv, fig. 2. 



