168 CRETACEOUS GASTROPODA 
canal, and a slightly twisted columella. The operculum is obovate, with a central, 
lateral, and internal nucleus. The animal does not seem to have been made known 
up to the present. It is possible that acquaintance with it may support Adam’s 
subsequent proposition, which remains only a question of time. I would, however, 
draw attention to the similarity of the shells and operculum of Pustonella with those 
of the czavaruztin#, a sub-family of the Przvroromipz. The general form of the 
shells does not exhibit any particular difference. Several of other Pzzvroromipz— 
Mangelia and Cythara,—have a totally similar structure of the shell, to what 
we find in Pusionella. The Pusionella Nifat, P. scalarina, and others have a 
distinct notch near the suture on the outer lip, and in all cases the posterior portion 
of the aperture is somewhat contracted or narrowed. The opercula are exactly 
the same in Pusionella and Clavatula, and it would not therefore be the least surpris- 
ing if the animals would show us, that Pwszonella belongs to the cravaruLin”. 
In the other sub-family—rzresrivz—Messrs. Adams distinguish two genera, 
Acus, Humphrey, and Yerebra, Adanson. If the animals were throughout so 
different as they are represented by the two typical forms in Adams’ Genera, it 
would be worth while to support these genera by some distinctions in the shells. 
But the former distinction as regards the position of the eyes does not seem 
always to exist, and the latter, relating to the existence of a posterior sutural 
eroove, tortuous columella, and anteriorly sinuated outer lip of Terebra as dis- 
tinct from Acus, is almost impossible to retain. If these distinctions are to be 
really of any great importance, it appears as if we should then occasionally 
regard specimens unquestionably belonging to one and the same species as not 
only specifically, but even generically different. We should besides form a number 
of other small groups or sub-genera to receive those species which have a sutural 
band but no anterior sinus on the outer lip, and those which have a twist- 
ed columella and the same entire outer lip, both being distinct from <Acus 
proper ; otherwise we had better not have entered at all upon a division of the 
genus Terebra. Gray rejects (Guide, 1857, p. 6) Messrs. Adams’ distinctions as 
to Acus and Terebra, uniting both under the former name. He adds, however, 
three other genera, Swbula, Leiodomus, and Dorsanum, the last of which seems 
scarcely different from Bullia. The animal of Leiodomus is sufficiently different 
from Terebra and from Bullia, but it is very difficult to distinguish the shells from 
the latter. Speaking of Subula, Dr. Gray refers to some figures (of Quoy and Gaimard 
in Mrs. Gray’s collection) which contradict his own characteristics. From all these 
remarks it will be sufficiently clear that we must wait for some time until the 
examination of the animals of Zerebra has so far advanced as to support any 
proposed distinctions in the shells. 
It remains finally to say a few words as regards the place which we have 
assiened here to the Tzrasrrpx. We confess that it was almost accidental that the 
family has been treated here, because we could not find any other better or more 
appropriate place for it before. The natural relations to the CancrrrarrD# on 
the one and to the PrraurprLLips# on the other side would scarcely have called 
