1895.] NATURAL SCIENCES OF PHILADELPHIA. 237 



OBSERVATIONS ON THE DENTITION OF ACHATINELLIDiE. 



3Y H. M. GWATKIN AND HENRY SUTER, WITH PREFATORY NOTE 



BY II. A. PILSBRY. 



The dentition of the Ackatinellidce has already heen investigated 

 by Heyneraann 1 and by W. G. Binney. The latter author, in 

 co-operation with Thomas Bland, 2 has published several papers 

 upon the subject, and to him is due the credit of discovering that 

 within the group commonly known as Achatinella, two extremely 

 different types of dentition exist. 



The first, including Achatinella s. dr., Partulina and Tornatellina 

 is characterized by an excessively delicate jaw (which is completely 

 lost in potash preparations), and teeth arranged en chevron, in very 

 oblique transverse rows, all of the peculiar form shown in Plate XI, 

 fig. 52, and found also in Athoracophorus, etc. The shells of this 

 group are glossy or brilliant, and the animal is arboreal. 



The second type is seen in the groups Amastra, Labiella, New- 

 combia, Laminella and Leptachatina. Here the jaw is stronger, 

 arched, and smooth or striate. The teeth are arranged in nearly 

 straight transverse rows, and are of the type found in Achatina and 

 Rumina, differing from the teeth of Helicidse in the narrowness of 

 the rhachidian row (see PI. XI, fig. 56). The shell is dull in the 

 majority of the species of this group, and the animal is in most 

 cases terrestrial in habit. 



Allied to the last in dentition, but distinct in its strongly .ribbed 

 jaw, is the genus Carelia, which thus constitutes a third primary 

 group of Achatinellidse. 



These three groups are, there can be no reasonable doubt, of 

 generic rank, and will bear the following names: 



1. Genus Achatinella Swainson, 1828. Contains the sectional 

 divisions mentioned above, with some others. Of this generic term, 

 Helicter of Pease and Fischer is a synonym. There is no reason - 



1 Malak. BL, 1869. A. bulimoides. 



2 Annals of the Lyceum of Nat. Hist of New York, X, p. 331, 1873; Ibid. 

 XI, p. 190; Annals of the N. Y. Acad. Sciences, III, pp. 96, 103. 



