108 GASTEROPODA OF THE INFERIOR OOLITE. 



with a stout diverging pair of spines, or didactyl wing. Other indications are 

 wanting. 



Relations and Distribution. — This species seems to be the descendant of the 

 short variety of Sp. didactyla. A single specimen was found in the Sauzei-bed, 

 or marl with green grains at Oborne. 



Genus — Alaria, Morris and Lycett, June, 1851. 



" Shell fusiform, turrited ; anterior canal straight or curved ; lip dilated, digitate 

 or palmate, formed by the prolongation of the last whorl ; no posterior canal ; no 

 sinus properly so-called on the anterior margin of the Up ; columellar margin not 

 callous." — Fischer. 



The above diagnosis is substantially that of Piette (' Cont. de la Pal. Franc.,' 

 p. 16), who adopted Morris and Lycett' s genus with modification. Piette further 

 alludes to the nakedness of the first whorls, which are smooth and convex, and 

 also to the power of developing varices, spurs, and protuberances at various periods 

 of increase, evident traces of rudimentary wings, which appeared usually on the 

 side opposite the actual (definitive) wing. 



This very important genus has been variously subdivided into sections, to say 

 nothing of sub-genera, such as Spinigera previously described. On the other 

 hand, as already observed, there are not wanting those who fail to see any generic 

 difference between Alaria and Aporrhais (Chenopus). Into these questions I do 

 not feel disposed fully to enter, being on the whole satisfied that the genus Alaria 

 may fairly be taken to cover the remainder of the wing-shells of the Inferior 

 Oolite, with possibly one or two exceptions. It would not be difficult for a casuist 

 to prove, almost to demonstration, that the family of the Aporrhai'das consists of 

 little more than one genus. Thus Cossmann makes Malaptera (in part the old 

 Jurassic Pterocera) co-generic with Aporrhais, which Gardner says does not differ 

 from Alaria, of which Spinigera, according to Fischer, is merely a sub-genus. As 

 was urged in the Introduction to this memoir, since the practical acceptance of 

 the doctrine of evolution we no longer worship the fetish implied in such terms as 

 "species," "genus," "family," &c. If no lawyer is able to draft an Act of 

 Parliament through which some other lawyer cannot drive a coach-and-four, how 

 much more applicable is this principle to the diagnosis of shells. 



As far as the shell goes we need not, I think, have much difficulty in separating 

 Alaria from Aporrhais in the majority of cases, since the wing in Alaria is barely 

 or, at best, but scantily palmate, and does not envelope more of the spire than the 

 anterior half of the penultimate. The monodactyl Alarice are widely different from 



