ALARIA. 109 
Aporrhais, and, if we except certain obscure forms with no wing attached, the 
monodactyls seem to have been the earliest Aporrhaids. Even the didactyl Alarie 
have the wing but scantily palmate, and not embracing. In the Great Oolite, 
however, there are forms such as ‘ Pterocera”’ atractoides, Desl., where the wing 
becomes more complex and embracing; and here the resemblance to Aporrhais 
becomes effective. Hence Piette places this species under Aporrhais. When we 
come to the malacology of the subject, attempts at comparison resolve themselves 
mainly into conjecture, as far as the Jurassic Aporrhaids are concerned. These 
may have been the ancestors of part of the Strombidz as well as of the modern 
Aporrhaidz, and probably differed from both to a certain extent. Piette divided 
the Jurassic Alarie into five sections, viz. Varicifers, the Monodactyls, the 
Adactyls, the Longicaudes, and the Hamicaudes. To simplify matters these might 
be placed under two grand divisions. We do not, in this country, appear to have 
the section “* Varicifer ”’ developed, as far as I can understand it ; the Monodactyls 
proper are numerous and important, whilst the Adactyls may owe their wingless 
appearance to various causes. All these I propose to place under the first grand 
division, assuming that they either have, or might have, no more than one digita- 
tion when there is no evidence of a second. Our first grand division, then, is 
constituted by the Monodactyls. 
The Longicaudes, which are almost coextensive with the mywrus-group, and the 
Hamicaudes, which are almost coextensive with the trifida-group, make up the 
second grand division. The shells of both these groups, when mature, develop two 
digitations on the wing. These are Didactyls. There will still remain one or two 
forms somewhat difficult to place. 
It is probably true that more species are made out of these fossils than would 
be the case if all the specimens could be obtained in a reasonably perfect condition, 
like the shells, for instance, of existing species of Aporrhais. But if we were to 
wait until none but perfect specimens of Alaria were accepted, the Jurassic Apor- 
rhaide might as well be left alone. Owing to the number of processes which many 
of these curious shells possessed, their preservation is rarely complete, and it thus 
happens that what ought to be recognised as the same species presents such a 
different aspect under the various conditions under which it is found as to make its 
recognition very difficult. To avoid error altogether under the circumstances is 
almost impossible. ‘Too often we have to choose between the Scylla of a doubtful 
identification and the Charybdis of ‘‘ species-making.” 
Thus the first forms described and figured in Pl. IV are wingless, and mostly 
without the canal-sheath. It becomes necessary to distinguish these in some way, 
yet such “species’’ are little more than tentative. The bulk of the species are 
described with some attempt at grouping. 
