26 CRETACEOUS GASTROPODA 
the canal. I have consequently referred only those species, in which I have been 
able to observe such marked callosity—differences in the aperture and the canal 
to Aporrhais, and have left the others provisionally in Alaria. I am quite 
aware of the weakness of this point; still I cannot think it right to consider 
all distinction as d@ priori impossible, and thence to unite all under the genus 
Aporrhais, as has been done by Professor Pictet. My chief reason for not 
doing so, is my fear lest by this system all chance of progress in a classificatory 
knowledge of the numerous fossil dzara should be cut off. It is, for example, 
difficult to understand, that species like #. carimata, Mant. or Anchura abrupta, Conr. 
ought to be brought into closer alliance with Aporrhais, than with Rostellaria, 
They differ from both, but I should say more from the former than from the latter. 
The genus Alaria must be in some way restricted, and cannot be retained either in 
the sense in which it was introduced by Morris and Lycett, nor as lately com- 
mented on by Piette. Chenu classed Alaria with Pterocera, but very different forms 
appear to be represented in it, allied to Rostellaria, Pterocera and Aporrhais, 
Deshayes in the last issue of the Coq. foss. de Paris, Tom. IIT. p. 488 also entertains 
the opinion, that Alaria (certainly in part) is more allied to Rostellaria than to 
Aporrhais (Chenopus). 
I have repeatedly gone over all the fossil species known to me, and it is, I 
think, impossible to come at the present to any satisfactory arrangement. Much 
may be expected from good materials, since scarcely one-tenth of the species, known 
up to the present, have been obtained in a perfect condition. Still, for along time 
to come, nothing but an artificial division will answer; I mean, a division based more 
upon one or other single character, than upon the totality of the structure and 
form of the shells. The following may serve as an attempt, at least in one direction, 
though I confess I myself look at it for the present partially hopeless of success, 
and I do not like, therefore, to carry it out. 
These remarks refer principally to the forms, which have been formerly noted 
as Aporrhais or Rostellaria. The relations between the latter genus and Pterodonta 
will be noted subsequently in detail. 
1s¢.—To restrict the name Alaria to the species with a simple. undivided and 
narrow wing, as the Jurassic Al. hamus, Desh. and Al. rhinoceros, Piette 
and Desh. 
2nd.—Species, which have the exterior termination of the wing extended 
in two opposite directions (as Lost. carinata, Mant.), and possess a 
long anterior canal, could form a small group, designated by Conrad 
Anchura.® 
3rd.—Broad winged shells with only a single point to the posterior external 
termination, as Rost. Orbignyana, Pict., or Lost. papilionacea, Goldf. 
might be distinguished under a separate name. 
* Jour. Acad. Nat. Sci. Philad. TV, 284, Pl. 47, Fig. 1. Conrad’s characteristics are very closely specified 
and restricted to the single species, which he describes, 
