80 On the Lingual Dentition of 



its entire length, no interstices being left between the plaits. 

 As the word plait would imply an actual folding of the sub- 

 stance of the jaw upon itself, we have not used that term, as 

 there is in reality a simple thickening. In using the word 

 plate, we do not intend to describe the jaw as composite, as in 

 the case of Orthalicus, or Achatina fasciata and virginea, in 

 which it seems to be composed of separate, i. €., partially de- 

 tached plates, imbricated one upon the other, with oblique 

 sutures, those of the upper centre chevroned upon the central 

 line, so as to leave an angular upper central plate. From this 

 angular plate is derived the term Goniognatha used by Morch 

 for one of the sections into wliicli he suggests the Geophila may 

 be classified according to character of jaw. In the jaw of H. 

 turhiniforinis the central plates are perpendicular, with no 

 approach to the angular arrangement. The plates must be 

 considered, therefore, as a modification of the rib-like process, 

 which characterizes most of tlie species of the genus Helix, as 

 restricted by Albers and v. Martens, but by no means all of 

 them, as we find a ribless jaw in H. alternata, Heinphilli^ 

 striatella, asteriseus, labyrinthica, Phoenix, tnuscarum, and 

 vartans, in the last of which we have also a highly developed 

 median projection. 



With the exception of the absence of angular plates at the 

 upper centre, this jaw resembles very closely that of Cylindrella 

 rosea (see photograph, Amer. Journ. Conch. Y., plate XI,), or 

 that of Pineria Schrammi (Ann. Lye. N. Y., X. 22). 



We now notice, for the first time, this form of jaw in the 

 Genus Helix, in which stout, distinct ribs are usually found 

 upon the anterior surface of the jaw, decidedly crenellating 

 either margin. It is very common, however, in the genus 

 Buliniuhis, having been observed by us in B. aurisleporis, 

 Brug., suffiatus, Gld., membranaceus, Ph., papy^'aceus, Mawe, 

 Jonasi, Pfr., alternatus, Say, jpallidior, Sow., and aureolus, 

 Guppy, var. Rawsoni, In the jaw of B. aurisleporis there 

 appear to be angular central plates. 



