LAMELLIDENS. 179 



Var. cylindrica (Hanley $ Theobald) Simpson, Washington, 

 D.C., Smiths. Inst., Nat. Mus. Proc. xxii, 1900, p. 855. 



Unio marginalia var. cylindrica , H. & T., C. I. 1876, p. 20, pi. 44, 

 fig. 1. 



As hitherto the name has been a mere nomen nudum, and no 

 specimen actually corresponding to Hanley & Theobald's figure 

 being available the following short description of the figure itself 

 may be given : 



Eather more rectangular than the typical form, dark olive- 

 green, concentrically banded, especially towards the ventral margin 

 and posterior side, with yellowish brown, and transversely rayed 

 from the umbonal region with dark olive-brown ; interior of shell 

 salmon-coloured. 



Long. 44, lat. 10-2 mm. 



Hob. ? 



Var. hanleyi, Simpson, Washington, D.C., Smiths. Inst., Nat. 

 Mus. Proc. xxii, 1900, p. 855. 



Unto marginalia var. corrictna, H. & T., C. I. 1876, p. 20, pi. 44, 

 fig. 4. 



Shell more or less indented in the middle, sometimes elongated 

 cylindrical, sometimes compressed and oval-oblong ; cardinal 

 callosity (which is rarely absent) more or less developed ; anterior 

 or hinge teeth almost horizontal, outwardly curved, rather more 

 elongate, or if shorter, rather more prominently elevated. 



Long. 42, lat. 89 mm. (fig. in Con. Ind.). 



Sab. Calcutta, etc. 



Subsp. thwaitesi (Lea). 



Unio thwaitesi, Lea, Proc. Acad. Nat. Sci. Philadelphia, iii, 

 1859, p. 152 ; Journ. Acad. Nat. Sci. Philadelphia, iv, 1860, 

 p. 246, pi. 37, fig. 125 ; Obs. Genus Unio, vii, 1860, p. 64, pi. 37, 

 fig. 125 j Keeve, Conch. Icon, xvi, 1865, pi. 23, fig. 105; H. & 

 T., C. L 1876, p. 20, pi. 43, fig. 1 ; Paetel, Conch. Sain, iii, 1890, 

 p. 169. 



Margaron ( Unio) thwaitesii, Lea, Syn. 1870, p. 74. 



Unio consobrinus, H. & T., C. I. 1876, p. 19, pi. 41, fig. 7. 



Lamellidens thwaitesii (Lea), Simpson, Washington, D.C., Smiths. 

 Inst., Nat. Mus. Proc. xxii, 1900, p. 856. 



Original description : Testa laevi, regulariter elliptica, sub- 

 inflata, inaequilaterali ; valvulis crassiusculis ; natibus prominulis ; 

 epidermide castanea, polita, transverse fasciata ; dentibus cardi- 

 nalibus valde compressis, lamellatis, valde obliquis, in utroque 

 valvulo duplicibus ; lateralibus longis, lamellatis curvisque ; 

 margarita salmonis colore tincta et iridescente. 



Hob. Ceylon (Thwaites). 



