254 APORRHAID^E. 



fold long and narrow : operculum slighter than that of A.pes- 

 pelecani, but agreeing with it in other respects. L. 1'2. B. (to 

 the furthest spike of the pterygoid flap) 1. 



HABITAT : Muddy sand in 40-85 f. on the east coast 

 of Shetland, at a distance from land of 650 miles 

 (M.' Andrew, Barlee, and J. G. J.) ; it is gregarious, 

 although very local. M f Andrew and Barrett dredged a 

 single dead specimen off the coast of Upper Norway, at 

 a depth of 70 f. ; but no Scandinavian zoologist appears 

 to have met with it. 



This mollusk is not so inactive as its associate, A.pes- 

 pelecani. Its faeces are oval and brownish. Mon- 

 strosities of the shell sometimes occur : one has the top 

 spike double or forked, another has four digitated pro- 

 cesses on the outer lip, and in a third the top spike is 

 attached to the lower five whorls. Some specimens are 

 much smaller than others; I have given the average 

 dimensions. 



A. pes-carbonis of Brongniart (a fossil of the upper 

 Miocene formation of Bordeaux and Antwerp) is equally 

 small, but a much stronger shell ; and the basal process 

 is short, spear-head-shaped and incurved, as in A. pes- 

 pelecani. The present species differs from A. Serresiana 

 (a Mediterranean shell) in its smaller size, delicate tex- 

 ture, fewer and rounded (instead of angulated) whorls, 

 and in the spire being much less tapering. Size alone 

 is, of course, not an infallible criterion of distinctness 

 especially if we take into account the depth of water and 

 distance from land ; but it is remarkable that Zetlandic 

 specimens of Pecten aratus (P. Bruei], P. Testa, P. 

 septemradiatuSj var. Dumasii, Tellina balaustina, and 

 many other species are larger than those from the south 

 of Europe. If Philippi had not described his Chenopus 

 desciscens (a Palermitan and Calabrian fossil) as having 



