BITHINIA. 17 



tions are the bane of our .science, and tend more than any 

 other cause to burthen Natural History with an oppressive 

 and confusing mass of synonyms. 



This little shell has an ovate-acute figure, and is thin, 

 semitransparent, and of an uniform horn-colour. Its sur- 

 face has a satinlike gloss, and is usually smooth ; occa- 

 sionally, however, the lines of increase become strongly 

 indicated upon the base, and a few obsolete spiral ridges 

 are barely perceptible towards the outer lip. There arc 

 from four to five tumid and deeply divided volutions, that 

 slope inwards at their lower extremities, and instead of 

 gradually shelving from the suture above, stand out from 

 it abruptly and subrectangularly, so as to produce a kind 

 of scalariform appearance. The whorls enlarge rather 

 quickly from a not very fine and acute point ; yet the 

 body or final coil is short in proportion to the preceding 

 one, and when viewed dorsally does not exceed the length of 

 the spire. The base of the shell is rounded, yet compressed. 

 The mouth, which is not contracted to an acute angle 

 posteriorly, is obliquely subcircular, but is rather longer 

 than broad ; it occupies three-sevenths of the total length of 

 the shell, and decidedly more than half the basal diameter, 

 since it projects outwardly much beyond the columnar 

 axis. The peristome is acute and continuous, but disposed 

 to expand ; it curls back a little so as partially to conceal 

 the small but distinct umbilicus. The outline of the outer 

 lip is more or less sinuous. The ordinary length of the 

 shell, which is twice its breadth, is a quarter of an inch. 



The animal is grey, slightly speckled with orange ; its 

 head and neck are dusky grey, the tentacula very long, 

 greyish- white, and ringed with orange in the region of the 

 eyes. The foot is pale-greyish white. The denticles of the 

 tongue are not so prominently crenated as in the last species. 



VOL. HI. D 



