GENERIC ALLIANCES. 85 
Nassa than Bullia: it has a thickened lip, a plicate columella, and 
the inner lip is toothed. Bullia differs from Nassa in the animal 
having no eyes; but the parallel series of forms is so extensive as 
to suggest that some examples of Bullia are only eyeless forms of 
Nassa. Notwithstanding the fact that, as vegetable feeders, the 
Rissoze have been placed at a great distance from the Nasse in 
most modern arrangements, they present numerous points of 
resemblance ; many of the shells are miniature representatives of 
the larger Nassz, and the canal at the base is rudimentary in several 
Nasse. 
The N. rissoides, Marr., very closely borders on the genus Rissoa. 
The genus Nassaria, Link, is composed of Nassze with elongated 
canals, and the N. pagoda, Reeve, is an intermediate form. 
The Northia serrata has so many characters in common with 
the elongated forms of N. trifasciata, Gmel., that it is difficult to 
see how they differ ; they are similar in texture, in colour, in having 
the upper whorls cancellated, in having a thickened outer lip, and 
in having sharp, prickly serratures on the edge of the lip. Several 
shells, placed by some authors among the Strongylocera, Morch., 
and by H. and A. Adams in a sub-division of the Nassz (Uzita), 
are intermediate in their characters between Nassa and Purpura ; 
they consist of the N. pallida, Powis., Reeve, pl. 9, f. 30; Buce. 
Gaulterianum, Kiener, plate 19, f. 70.; N. plicosa and Morrisii, 
Dunker, &c.; and the Purpura nassoides, Quoy. and Gaim., is a 
nassoid form of Purpura. 
The N. varicifera and N. scalaris, A. Adams, show an affinity 
with the genus Scalaria, or Scala, as it is shown to be by priority. 
Many of the shells placed in the genus Columbella are difficult 
to distinguish from this genus (Nassa). The hard and fast lines 
drawn tightly round certain genera are much simpler to recognize 
on paper than when observation is brought to bear upon them 
practically. I have had considerable difficulty in determining to 
which of the two genera some of my shells belong, and many of my 
conclusions regarding them have been anything but satisfactory. 
The two genera glide so imperceptibly into each other that it 
is impossible to separate them. 
