100 GASTEROPODA OP THE INFERIOR OOLITE. 



more than one-third the size, is wider-angled, and has a flatter base ; the notch also 

 is probably wider and more distinct. There is an undescribed species of Brachy- 

 trema in the Bajocian of Normandy (for a specimen of which I am indebted to the 

 generosity of M. Deslongchamps), which greatly resembles this form, and also B. 

 Wrightii, but yet has points of difference from both. These differences are probably 

 not more than varietal. B. Wrightii and its allies represent the group of Brachy- 

 tremas which are related to Purpuroidea. In the well-preserved specimens of the 

 French Bajocian it is possible to note this relationship. 



The variety despecta is founded on a unique specimen from P 3 , Vitney Cross 

 (see p. 38), and is the only Brachytrema that has hitherto to my knowledge been 

 found in the Inferior Oolite of England outside of the Lincolnshire Limestone. If 

 additional evidence as to its differing materially from B. Wrightii should be 

 obtained, the species may be known as Brachytrema despectum. 



Family APORRHAID^E. 



" Shell turrited, aperture continued in front by an imperfect canal or a groove ; lip 

 expanded, aliform or digitate." — Fischer. 



The Inferior Oolite, in England, contains three genera, which may be referred 

 to this family, viz. Malaptera, Piette, Spinigera, D'Orbigny, and Alaria, Morris 

 and Lycett. These genera are probably of unequal value, and it might perhaps be 

 difficult to give a very rigorous and logical definition of any one of them, so linked 

 are they to all appearance by connecting forms. Besides the three named genera 

 there are one or two species of the Aporrhaiidae, which seem rather difficult to 

 place under any of the above. 



The Cretaceous Aporrha'idge have received a considerable amount of atten- 

 tion from Mr. J. Starkie Gardner, 1 and, in common with some other concho- 

 logists, he failed to see any difference of generic value between Alaria and the 

 existing Aporrhais. However, Fischer clearly endorses Piette's view as to the 

 propriety of keeping Aporrhais distinct from at least the bulk of the shells usually 

 referred to Alaria ; and the farther we go back in time, the more the Alaria-growp 

 predominates over the others, until its origin is lost in the small and often obscure 

 forms, which a minute and careful search is gradually revealing from the Lias. 



1 "On the Gault and Cretaceous Aporrhaidro," by J. Starkie Gardner, F.G.S., 'Geological 

 Magazine,' 1875. 



