1921. | B. PrasHapD: Gastropod Molluscs. 221 
much closer ; a reticulate pattern is also formed in some cases by 
the fusion of the stripes with one another. 
I assign all the Mesopotamian specimens to the var. aberrans, 
Dautzenberg (fig. 1c.), since the constriction on the body-whorl 
in most cases is quite absent or only faintly indicated. The speci- 
mens are, further, less elongate than the typical form and have a 
comparatively broader columellar area. The colouration is very 
vatiable. In some cases the shells are uniformly dark-brown or 
black, in others they have purple, red, chocolate or brownish wavy 
stripes alternating with much broader white stripes, while most of 
them show a distinct network of white spots alternating with 
coloured ones, the latter formed by the fusion of the stripes with 
one another. Most of the specimens are of a smaller size than those 
of the typical form. 
Family HYDROBIIDAE. 
Specimens of the genera Tvicula, Bithynia and Amnicola 
(Alocinma) are represented in the Mesopotamian collections before 
me. Dr. Annandale (loc. cit., p. 163) assigned an imperfect shell 
from Nasariyeh to the genus Lithoglyphus, Mihl., with some doubt. 
I have examined this specimen and agree with Dr. Anna.\dale in 
considering it as possibly belonging to the genus Lithoglyphus, but 
it is too imperfect for a precise diagnosis. 
Genus Tricula, Benson. 
1843. Tricula, Benson, Cal. Fourn. Nats iist., p. 407. —: 
1851. Bithinella, Moquin Tandon, Fourn. Conchyliol. Ul, p. 239. 
1852. Paludina (in part), Kiister, Mart., Chemn. Conch.—Cab., Palu- 
Gina, ebosyPs le 2 : 
1856. Bythinella, Moquin Tandon, Hist. Moll. Terr.—Fluv. France, 
Presbo: 
1858. Tricula, H. and A. Adams, Gen. Rec. Moll. 1, p. 300, pl. xxxi, 
figs. 5, 5a, 5b. 
1862. Tricula, Benson, Ann. Mag. Nat. Hist. X, pp. 415, 410. 
1863. Paludinella (in part), Frauenfeld, Verh. Zool.-bot. Ges. Wren, 
XIII, p. 199. 
1885. Tvicula and Hydrobia_ subgen. Bythinella (in part), Nevill, 
Hand-List. Moll. Ind. Mus. M1, pp. 62, and 49 respectively. 
1887. Tricula, Fischer, Man. Conchyliol., p. 727: 
1892. Sythinella, Kobelt, Rossmassler. /con. Eur. Moll. (n. s.), V, 
Pp- 36, 37: 
1915. Tvricula, Preston, Faun. Brit. Ind. Freshw.-Moll. p. 608. 
I have carefully compared shells of the Himalayan species 
Tricula montana, on which Benson founded his genus, with those 
of certain European species assigned by most recent authors to 
Bithinella, Moquin Tandon, and can find no generic difference. 
Kobelt’s figures of the various species of Bithinella, moreover, 
strongly support the view that the two are identical. A short 
review of the confusion that has existed in literature regarding 
the exact status of the genus Tvicula may be given before consi- 
dering the question of its synonymy. 
