50 J. Starkie Gardner — On the Gault Aporrha'idce. 



that the relationship to Scalaria is better seen and traced through 

 Aporrhais in fossil than in living examples of the family : some 

 fossils of the last-named genus, as will be seen, approach very 

 closely to Scalaria. 



Gwyn Jeffreys, in his British Conchology, 1857, describes the 

 Aporrhaidce as follows : — 



" Body spiral ; mantle large and loose, forming a very short 

 branchial fold at the partially channelled base of the shell, which it 

 lines ; snout cylindrical, contractile, notched in front ; tentacles awl- 

 shaped, separate ; eyes on bulgings or short stalks, at the outer base 

 of the tentacles ; foot small, lanceolate ; gills arranged in a single 

 narrow plume; odontophore enveloped in a sheath, straight; rachis 

 single ; pleura? or uncini three, plain-edged." 



" Shell, when young, spindle-shaped, never umbilicate ; spire 

 turreted and tapering ; mouth widely expanding ; operculum small, 

 horny, pear-shaped, increasing by semielliptical layers ; nucleus 

 nearly terminal at the base of the mouth." 



The animal differs from those of Bostellaria, Strombus, and Ptero- 

 ceras, in the eyes being at the base, and not at the extremity of the 

 tentacles, and in the tentacles not being bifurcate, etc. Models of 

 both may be seen in the British Museum. Its mode of growth is 

 similar to that of the Strombidce. "When young it developes in the 

 form of a cone or spindle, and increases in the usual manner of 

 spiral shells : but at a certain point it ceases to grow spirally ; a rib 

 of enamel appears along the mouth, the borders of which thicken 

 and contract ; the lip dilates, expands, and becomes cut up into 

 spikes or digitations till the outer lip is complete, when the subse- 

 quent growth takes place by adding fresh layers inside. 



In the young state it extremely resembles Cerithium and Scalaria, 

 a fact noticed by Swainson ; when the canal is developed, and before 

 the wing begins to grow, its appearance is that of a Fusus. 



Monstrosities are not uncommon, both in recent and fossil forms, 

 in the shape and size of the pterygoid process. 



The term Aporrhais was applied by Aristotle to probably what is 

 now known as A. pes-pelicani of the Mediterranean and British 

 seas, and was derived from the word ^Airoppea) " to flow out," and 

 was on his own testimony suggested by the spouted form of the 

 shell ; he also noticed the operculum {eTriKoKvpuxa or ircofia). 

 Aldrovandus and then Grualterius used the term for Lamarck's genus 

 Pteroceras. Petiver in 1711 restricted the term to shells of the 

 present family of Aporrliaidce. Da Costa in 1778 adopted it as a 

 generic appellation, but included it with Strombus, Pteroceras, etc., in 

 Lamarck's family of Alata. The term Chenopus was needlessly 

 introduced by Philippi in 1836, who, however, first rightly defined 

 and understood the characters of the genus, and has been frequently 

 used since. 



I have referred somewhat at length to the history and characters 

 of the recent family, as it is not separated from the Strombidte by 

 most conchologists ; and undoubted Aporrhaides are still sometimes 

 described as Bostellarias by geologists. 



