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Contributions to the Palaeontology of Gloucestershire : — On the 

 Strombidii' of the Oolites. By Thomas Weight, M.D. With 

 the description of a new and remarkable Pteroceras. By John 

 Lycett, Esq. 



Read 28th January 1851. 



Among the remarkable new forms of extinct gasteropodous 

 mollusca which have from time to time been brought under the 

 notice of the Members of this Society, there are none more in- 

 teresting or more valuable as contributions to the oolitic fauna, 

 than the winged shells belonging to the genera Pteroceras and 

 Rostellaria. 



The Strombida were first recognised as a distinct group of gas- 

 teropods by Lamarck, in which this learned zoologist assembled 

 several forms having affinities with each other in the singular 

 development of the outer lip of the shell ; with these he formed 

 his family des Ailees, which includes the genus Strombus of Lin- 

 naeus, and corresponds with the Strombida of modern naturalists. 



This family is well characterized by the form of the shell and 

 that of the animal. The shell in the young state is conical or 

 spindle-shaped ; after having grown in a regular manner for a 

 longer or shorter period of time, its farther development is ar- 

 rested, the outer lip becomes dilated, thickened and enlarged in 

 a very remarkable manner, and sends out often long digitations ; 

 the anterior part of the mouth terminates in a canal accompanied 

 with a more or less distinct sinus. The animal has the foot di- 

 vided into two parts, the one posterior cylindrical and obliquely 

 truncated and supporting a horny operculum. The other part is 

 flat, rounded before, and adapted for attaching the mollusk to 

 solid bodies. The head is large and thick, and is prolonged into 

 a bifurcate extensible proboscis ; the tentacula are large and di- 

 vergent, and carry the eyes at their extremities. In this family 

 are grouped the genera Strombus, Pteroceras, Rostellaria, Apor- 

 rhais, Chenopus, and Pterodouhi. 



The Strombida are first recognised in a fossil state in the dif- 

 ferent stages of the oolitic rocks. They are more numerous in 

 the cretaceous and tertiary strata, and have attained their greatest 

 development in the present creation. They are nearly all natives 

 of tropical seas, and are most abundant in the neighbourhood 

 of coral islands. 



