1893.] NATURAL SCIENCES OF PHILADELPHIA. 261 



constantly different from those of that species, prove it to be 

 altogether distinct. One of the main distinguishing features is 

 the presence of very fine, raised revolving lines on the nucleus, or 

 the 1? embryonal whorls, while those of V. pulchella are smooth. 

 The generally much more depressed spire, the deeper suture beside 

 the rather flatter whorls above, the last whorl more rapidly expand- 

 ing toward and descending to the aperture, especially at the suture, 

 the more approximate margins rendering the aperture nearly circu- 

 lar, are sufficient to distinguish costata from pulchella, even in the 

 absence of the membranous ribs, the most striking character of the 

 average shell. 



Our species, however, has these ribs and most of the other charac- 

 ters in common with several other forms, mostly found in Asia and 

 North America, while in Europe V. costata seems to be more iso- 

 lated. On the other hand, several of those related species seem to 

 be intermediate between this and the tenuilabris-cyclophorella, etc., 

 groups. All these forms need much more careful study. 



When seen under the microscope, the epiconch ("epidermis") 

 shows between the membranous ribs, 4-6 finer raised striae, and, in 

 addition, very numerous microscopic lines in a general radial direc- 

 tion, but mostly intercrossing in various ways, except near the 

 suture where usually they are parallel (Man. Conch., PI. 32, figs. 27, 

 28.) 



V. costata is quite variable, and a number of extreme forms must 

 be regarded as varieties. It may even prove to be difficult to draw 

 a line between this species and some others nearly related. In size 

 it averages 2"5 mm., few specimens measuring 2 - 7 or more, and the 

 smallest are 2"l-2 - 2. The number of whorls is almost constantly 

 Si, hardly more in the largest examples, and somewhatover 3 in the 

 smallest. There is variation also in the elevation of the spire — in 

 many specimens it is almost or quite flat and very low in the aver- 

 age. In those from Quebec, Canada, it is comparatively elevated. 

 As to the descending of the last whorl, it must be repeated that the 

 suture always descends more decidedly than the whorl in its totality, 

 and specimens are not scarce in which the back of the whorl keeps 

 nearly or exactly horizontal to the very margin, as in V. parvula 

 (Man. Conch, fig. 25, PL 32). Some diversity is also found in the 

 size and closeness, or number of the ribs : I counted from .23-35 on 

 the last whorl in different specimens which may be regarded as 

 typical. The lip also is variable, but always rather strong, and 



