116 Dr. T. Wright on the StrombicUe of the Oolites, and 



Pteroceras, Rostellaria and Chenopus are the most ancient 

 genera of this family ; they are still represented by numerous 

 species all different from those found in a fossil state. A few 

 species of Strombus have been found in the chalk ; more have 

 ben met with in the different stages of the tertiary period ; but 

 this genus has attained its full development in the seas of the 

 warm regions of our time, where the species are remarkable for 

 their gigantic size, singular forms, and rich and varied colour- 

 ing. Pterodonta has been found only in the chalk. Soon after 

 Lamarck had formed the new genera of his family des Ailees, 

 De Montfort* proposed his genus Hippocrena for the species 

 included by Lamarck in the genus Rostellaria which had the 

 labrum simple and dilated, the columella callous and forming a 

 channel conjointly with the labrum, which ascends close to the 

 volutions of the spire almost to its apex, the external lip with a 

 simple straight wing inflected towards the base, and with a short 

 pointed canal. He cited Rostellaria macroptera from the Barton 

 clay as the type of his new genus, which however has not been 

 adopted. 



Philippif recognised anatomical differences between the ani- 

 mal of Rostellaria curvirostris and that known as R. pes-pelicani ; 

 the latter has the eyes situated sessile on the sides of the tenta- 

 cula, while in the former they are terminal and retractile ; these 

 with other zootomical characters induced him to propose the ge- 

 nus Chenopus for R. pes-pelicani and other allied species : it is 

 just to observe, however, that Aldrovandus in 1623 described this 

 typical species under the generic name Aporrhais, which is now 

 adopted by British naturalists. 



The living forms of Chenopus have the respiratory canal de- 

 pressed and slightly channelled, and the labrum strongly digi- 

 tated, whilst in Rostellaria the respiratory canal is much grooved 

 and arched backwards, and the digitations when present are for 

 the most part long, slender and flexuous. Many fossil shells 

 from the oolitic and cretaceous rocks appear to occupy a position 

 intermediate between these genera, and ought probably to be 

 separated into a distinct genus ; this in fact was suggested, and 

 the genus Rostrotrema proposed, by Mr. Lycett, in a paper which 

 he read before our Society in August 1848, for the reasons that 

 the winged shells of the Oolite called Rostellaria differ from that 

 genus in " the absence of the upper or posterior siphon upon the 

 spire, the outer lip not extending beyond the body-whorl, or but 

 slightly upon the penultimate, and there being no corresponding 

 thickening upon the inner lip to form a channel." 



* Conchyliologie Systematique, tome ii. p. 523. 

 t Enumer. Molluscarum Sicilise. 



