J. Star Me Gardnei — On the Gault Aporrhaida. 51 



Morris and Lycett, in the Mollusca of the Great Oolite (Pal. Soc), 

 instituted a genus Alaria to receive those Jurassic forms which have 

 no posterior canal, with the left lip thin, never thickened ; left lip not, 

 right lip sometimes, extended on penultimate whorl. Many Cretaceous 

 forms, however, have a rudimentary canal, which would make it 

 embarrassing to adopt the character as generic, and would cause 

 nearly identical species to be separated, and thus break up natural 

 groups. M. Piette distinguishes Alaria by the wing being applied 

 to the last whorl but one, and never adhering to the rest of the spire. 

 This character is not of the slightest generic importance in a shell 

 so subject to variation ; in recent species the pterygoid process is 

 sometimes attached to the second whorl, sometimes quite to the apex 

 of the spire. See PI. III. Fig, 15, A. pes-carhonis, recent. 



Mr. E.. Tate, in a paper in the Geol. and Nat. Hist. Eepertory, 

 1865, established a sub-genus Perissoptera, with A. occidentalis as its 

 type, to receive those species which have a nearly entire and broad 

 wing, prolonged into a recurved point, and attached to the last whorl 

 but one. This sub-genus has not been recognized by zoologists 

 in the case of A. occidentalis, and Mr. K. Tate included A. marginata, 

 which certainly is nearer A. pes-pelicani. A simple division into 

 groups will for the present meet all he seeks to establish. 



Aporrhaidw appear first in the Jurassic age, and reached their 

 greatest development in the Cretaceous seas ; the number of species 

 in this genus far exceeds that of any other Gasteropod at Folke- 

 stone, and individuals are so numerous that hundreds of casts may be 

 picked up in a few hours by the collector. The family decreased in 

 importance in Tertiary times, and are now, in common with many 

 other Cretaceous families, only represented by a few species. There 

 appear to be only three species known, yet they are types of the 

 largest Cretaceous group. 



The following may be taken as the characters of Aporrha'is of Da 

 Costa. Shell turreted, strong, moderately elongated ; canal at base 

 beak-like and shallow, never very long, differing in this respect from 

 most Cretaceous forms ; whorls numerous, variously ornamented with 

 nodules or striae; mouth angulated, outer lip expanded and thickened, 

 detached from the spire at upper part (not a constant character), 

 either simple or expanded into claw-like digitations, corresponding 

 to well-marked keels on the last whorl. 



With regard to the so-called British Cretaceous Pterocerata, I have 

 long felt that they were unnecessarily separated from the family of 

 Aporrha'idce, with which they are constantly found associated, and 

 with which I have always considered they have the greatest affinities. 

 The principal difference is in the length of the spire, the general 

 plan and ornamentation of the shell being similar. The attach- 

 ment of the posterior digit to the spire, which has chiefly led to 

 their being classed with Pterocera, is no longer a character by which 

 they can be separated, as the figure (PI. III. Fig. 15) of a specimen 

 of A. pes-carbonis in the British Museum clearly shows. This figure 

 is very similar in arrangement of the digits, canal, and ornamen- 

 tation, to the fossil shown in Fig. 2. On the other hand, the aspect 



