ABIDA. 265 



the names quinquedentata and similis) appear also in his list 

 of species having the Chondrina type of teeth. Both species 

 have been investigated by Schako and by the author. They 

 belong unquestionably to Chondrina. P. muhlfcldii is stated 

 by Schako to have teeth like avenacea, and is therefore a 

 Chondrina. Pupa secalc, which Prof. Gwatkin has in his list 

 of species with teeth like Chondrina megacheilos, certainly be- 

 longs to the normal or Abida group, as I have examined sev- 

 eral radulas. It has a simple mesocone alone on the centrals, 

 but all the laterals have the ectocone, though smaller than in 

 some other species. There are about 12 laterals, of the broad 

 quadrate type. In Chondrina the laterals are more numerous, 

 narrow, with single long, curved cusps. A. frumentum has 

 fewer laterals, 5, with larger ectocones, and there are very 

 weak ectocones on the centrals. 



Apertural Teeth. 



Most species of Abida and Chondrina possess a special 

 lamella peripherad of the inner end of the parietal lamella, 

 called the spiral lamella; shown at s in pi. 42, fig. 4, also in the 

 other basal views on that plate, and in pi. 43, fig. 1, and 

 others. The spiral lamella is a disjoined portion of the an- 

 gular lamella, with which it is continuous in some species. It 

 is often absent. Although first noticed by Kiister many 

 years ago, most authors have ignored it, thus losing a useful 

 character. It may generally be seen in an oblique view in the 

 mouth, though of course not in the usual ventral view given 

 in figures. In some cases it is not visible without breaking 

 flie shell (as in pi. 43, fig. 1). 



The angular lamella is often duplicated or twinned by the 

 development of an accessory lamella outside of it, towards the 

 suture, shown in plate 42, figs. 8, 14, 16. In some species 

 there is a low lamella at the columellar end of the parietal 

 wall, as in pi. 43, fig. 14. Abida polyodon has a parallel 

 lamella, situated between the spiral lamella and the suture, 

 on the parietal wall, shown in pi. 44, fig. 3. The principal 

 lamellas and plicae of these genera are otherwise placed exactly 

 as in Gastrocopta, etc. There is more or less thickening or in- 



