1g21.| B. PrAsHaD : Gastropod Molluscs, 219 
already in the Indian Museum, makes it possible to discuss the 
individual variation in form and colour. 
Sowerby ! figures three shells of what he calls the three varie- 
ties of N. yordant, without indicating a typical form; his figures 
also are very poor. Reeve’s® figures show a rather ovoid shell 
with a relatively small and scarcely exserted spire and with the 
body-whorl nearly smooth or with only a slight constriction on it. 
Mousson did not figure the shells he examined, but described a 
new variety under the name turris, which he distinguished from the 
typical form by its much larger size, more elevated apex, which 
makes the shell almost subcylindrical in shape, and by the body- 
whorl having a more prominent constriction. The figure of the 
typical form, the only one illustrated in von Marten’s monograph, 
differs from that of Reeve’s in having a comparatively shorter but 
more prominent spire, the columellar border narrower, the mouth 
relatively smaller and the constriction on the body-whorl much 
more pronounced. Dautzenberg, who followed Locard as to nomen- 
clature, added a new variety (aberrans), which, according to him, 
is distinguished by the almost complete absence of the constriction 
on the body-whorl and by its variable but different colouration. 
Kobelt has given good figures of the typical form and of var. ¢urrts, 
Mousson. His figure of the typical form is quite similar to that of 
von Martens. Preston does not add any notes on the specimens 
examined by him, but says in his account of T. michoni that some 
of the specimens of this species link up the two species, T. jordant 
and T. michoni, and that these two are probably extreme forms of 
the same species only. Annandale, however, refers to some of the 
shells from Palestine and reported on by Preston as belonging to 
the var. turvis of Mousson. In view of the above remarks it is 
clear that we have to deal with three forms. (i) N. jordani s.s. 
which von Martens’ and Kobhelt’s figures may be taken to re- 
present, and which appears to be a tiue lake-form occurring in the 
Lake of Tiberias and probably in the Lake of Homs. (ii) N.jordanz, 
var. turris, described by Mousson and of which Kobelt’s figure is a 
good representation. ‘This form is stated to have been taken in the 
Lake of Tiberias, but the exact biological conditions under wnich 
it was found are not stated by either Mousson or Kobelt. In Dr. 
Annandale’s collections and those of the late Dr. Anderson from 
those areas the form is only represented in the collections from 
the exit of the River Jordan. The form is probably a true stream 
phase. (iii) N. jordant, var. aberrans, described by Dautzenberg, 
but of which no figures have been published. The type speci- 
mens of this form were collected in the Lake of Homs and all the 
specimens from Mesopotamia in my opinion belong ton tt. his 
form appears to be confined to closed or slow-running waters. 
The three phases discussed above may be distinguished by the 
following key :— 
| Conchological illustrations, Neritina, pp. 4, 6, fig. 49 (18.41). 
2 Conch. Icon., Neritina, species 129 (1856). 
