80 



LAND AND FRESHWATER 



NiLGiRiA BisTRiALis, Bcck. (Plate LXXXI. figs. 4, 4 a.) 



Nanina bistrialis. Beck, Index Moll. p. 2 (no description) ; Pfr. 

 Mon. Helic. vol. i. p. 71 : as diaphana, Lea, and exilis, Chemn. ix. 

 1831. 



Helix bisfriaUs, Eeeve, Conch. Icon. fig. 483; Conch. Ind. p. 14, 

 pi. xxix. fig. 1. 



Hemiplecta (sec. C) bistrialis, Theobald, Cat. L. & Freshw. Moll. 

 Ind. p. 22. 



Hemiplecta ? bistrialis, Blanford, A. M. N". H. Feb. 1863. 



Xestina, Pfr. Jahrb. v. p. 257 (1878) : type X. siamensis, Pfr. 



Xesta bistrialis, Semper, B,eis. Philipp. p. 64, pi. iii. fig. 15, 

 pi. vi. fig. 25 (1870). 



Xanina (Xesta?) bistrialis, Xev. Hand-list, 1878, p. 51. 



In Mr. W. T. Blanford's collection (No. 47. 1) there is one 

 specimen from Ceylon. 



Original description : — " T. subperforata, globoso-depressa, tenuis, 

 fragilis, subtilissime striata, striis confertis obsoletis sub lente decus- 

 sata, straviineo-cornea, lineis 2 7'ujis approximatis medio cincta ; 

 spira vix convexa ; anfr. 4, planiuscidi, rapide cresce^ites ; apertura 

 ampla, limari-ovalis ; perist. simplex, margine columellari recur- 

 vato. 



" Diam. maj. 34, miu. 25 : alt. 15 mill. 



" Habitat prope Pondicherry ; Tranquebar." 



Locality. Madras (Dr. Thurston). 



The mantle margin is quite plain ; no shell-lobes ; the neck -lobes 

 are as in N. tranqueharica (fig. 3). 



The jaw (PI. LXXXII. fig. 5) is slightly arched, with a flatly- 

 curved central projection. The central teeth (fig. 5«) are all 

 tricuspid and on broad plates, narrowing at the 18th and 19th-20th 

 (fig. 5 b), losing the side cusps gradually and becoming stoutly 

 aculeate, and the laterals are long and aculeate, becoming very 

 minute on the outer edges (fig. 5 d). They are arranged thus — 



50 . 2 . 17 . 1 . 17 . 2 . 50 

 69 . 1 . 69 



The genitalia (fig. 4) compare well with those of solata and tranque- 

 barica. The diverticulum of the male organ is not so long as in the 

 latter. The spermatheca is a globular sac on a short broad stem. The 

 amatorial organ is very elongate and twisted, the sharp turn near 

 the basal point being nearly at right angles to the succeeding 

 portion. It has a central muscular hard rod, terminating in a fine 

 point (fig. 4 o), covered successively externally by close-fitting 

 cases, through which the point is extensible. Strong retractor 

 muscles are seen near the base, and another at the extreme or 

 posterior end. 



The acquisition and dissection of tranqueharica and bistrialis have 

 shown that both these species must be also included in Xilgiria, for 

 in nearly all principal characters they agree with those of X. solata, 

 with the exception of the aculeate teeth of radula in hisfrinlis. 



