i2. B. Newton — On the Genus Leveillia. 203 



LeveilJia is therefore proposed to take the place of Leveille's genus 

 Porcellia. 



I may state that my colleague Mr. E. A. Smith, F.Z.S., the Con- 

 chologist of the British Museum, warmlj'- supports my action in this 

 matter, and fully admits the justice and desirability of removing 

 Porcellia from the list of molluscan genera. 



Genus Leveillia, E. B. Newton, nam. mut. 

 Porcellia, 0. Leveille, 1835, nan Latreille, 1804:. 



The chief characters of this genus may be briefly stated as : — Shell 

 nearly symmetrical, monothalamous, discoidal, biconcave ; whorls 

 contiguous and on the same plane, except initial ones, which are 

 slightly raised, and all exposed within a wide umbilicus ; the 

 dorsal area bears a narrow and centrally situated continuous band, 

 or groove, which opens on the external part of aperture in a slit ; 

 aperture oval or quadrangular ; surface structure beaded, ribbed, or 

 spirally striated ; umbilical margin round or angular, with a series 

 of nodulations or quite plain ; shell structure moderately thick. 



The distinguished Belgian palaeontologist, the late Prof. L. Gr. 

 de Koninck, published some extended observations on this genus 

 in 1843' and 1883,^ gi'^'ing a full synonymy and an emended descrip- 

 tion of the original diagnosis. 



Two species were described by Leveille in illustration of his genus, 

 viz. Puzo and IcBvigatn. The latter of these being without a slit, 

 De Koninck removed to Euomphalus in 1843, and finally to the 

 genus Straparollus in 1883, from which fact it is evident he con- 

 sidered the presence of the median band of the highest generic 

 importance, although Leveille failed to include it among his original 

 characters, recognizing it as only of specific value in his description 

 of L. Puzo, the type of the genus. The central position of this band 

 divides the shell into two equal parts. With the growth of the 

 shell the band becomes successively filled up until it reaches the 

 aperture where it is still open to form the slit. The slit itself is 

 often difficult to trace in specimens, but it is usually well seen in 

 the weathered examples from Tournay. Its special function would 

 no doubt be as in other fissured genera for the purpose of ejecting 

 vitiated water from the branchial chambers of the animal. 



Generic affinities. — In following the history of this genus we find 

 that much misconception has arisen as to its proper position in the 

 Mollusca. Many of its species have been ranked with the Cephalo- 

 poda under Ammonites, Nautilus, Goniatites, etc., though the total 

 absence of septa or chambers is strong evidence against such 

 determinations. Others have been described as ScJiizostoma, 

 Bellerophon, and Pleurotomaria. With regard to the first of these 

 genera, it may be stated that, possessing no slit, its other pecu- 

 liarities need not be discussed. On examining Belleroplion, or genera 

 known to be closely allied to it, we find it to be usually a heavy 

 globose and convolute shell, with a wide and semilunar mouth, 



• 1 Desc. Anim. Foss. Ter. Carbonif. Belgique, 1843, p. 357. 

 '^ Faune Calc. Carbonif. Belgique, 1883, p. 112. 



