86 



Family 4. ALATA. 



Shell ; emarginated or channelled at the base, outer lip expanded 

 or digitated at maturitt/, and more or less sinuated near the 

 base for the passage of the animar s proboscis-like head. 



The family Alata was instituted by Lamarck for the pui'pose of asso- 

 ciating in one natural group, the three genera Rostellaria, Fterocera, and 

 Stromhis, dismembered from the Linncean genus Stromhiis, and distin- 

 guished by that marked peculiarity of growth, which the shell of each 

 exhibits in the wing-like expansion of the outer hp, on arriving at maturity. 

 The researches, of subsequent naturahsts, aided by much increased zeal and 

 opportunities of studying the animal, have, however, discovered an affinity 

 with the above-named genera, in species arranged hitherto in a more remote 

 part of the system. The Aporrhais pes-PeVicam has long been generically 

 distinguished, and a difference has been recently observed in the soft parts 

 approximating to Struthiolai'ia, a genus necessarily transported to this family 

 by M. Deshayes upon the discovery of the animal by M. M. Quoy and 

 Gaimard, and I now feel it expedient, as indicating a link between Struthio- 

 laria and the Purpurifera, to introduce an important genus founded by 

 Dr. Beck, a distinguished naturahst of Copenhagen, under the name of 

 Priamus, upon a shell regarded by Lamarck and others as an inhabitant of 

 the land or marshes,''^ but now strongly suspected, if not ascertained, to 

 be living in the seas of Spain and Portugal. Were it not for the transition 

 afforded by the Aporrhais occidentalis, between StrMthiolaria and the 

 Lamai'kican Alata, I should have ventured to propose a new family for the 

 reception of that genus with Priamus ; but as the animal of the latter is 

 stiU unknown, the grounds for this separation are insufficient. 



The genera referable to this family are as follows : — 



Priamus. Aporehais. Pterocera. 



Struthiolaria. Rostellaria. Strombus. 



Genus 1. PRIAMUS, Beet 



Animal; unhioion. 



Shell ; oblong-ovate, ventricose, rather thin, diaphonous, some- 

 what horny or porcellanous, spire exserted, apex obtuse, a little 

 depressed, as if mamillary ; columella curved, truncated; outer 

 lip simple, effused, slightly sinuated towards the base. 



* Bullmus Priamus Bruguierc, Achaiina Priamns Lamarck, Helir Priamus Femssac. 



