228 PROCEEDINGS OP THE ACADEMY OF 



. Genus OKTHALICUS, Beck. 



Jaw composite, in numerous free, imbricated pieces, usually with 

 its sutures oblique to the centre of the jaw, leaving an upper, 

 angular, median piece; these pieces soldered together above. N 

 median projection to the cutting edge, which is serrated by the 

 lower angles of the separate pieces. 



The jaw of the only species within our limits, 0. undatus, Brug. 

 (pi. XVI., fig. 13) is of the type usual in this genus and Liguus, but 

 up to the present time never observed in any other genus. It is 

 composite, its separate pieces being apparently soldered firmly at 

 their upper portions, where, indeed, they seem collectively to form 

 a jaw in a single piece as in Helix, etc., but at their lower portion 

 positively detached and free, imbricated one upon another. The 

 jaw may in one sense be said to be in a single piece, as argued 

 recently by Messrs. Fischer and Crosse (Moll. Mex. et Guat.), 

 but with equal correctness it may surely be said to be composite, 

 as the amalgamation of the upper portion is produced by the 

 joining of absolutely separate pieces. There are seventeen of 

 these plates in the jaw figured, though the number varies, the 

 upper central one apparently lying upon the adjoining ones, which 

 are broad and extend from the upper to the lower margin of the 

 jaw. The jaw is strongly arched, with attenuated, blunt ends. 

 There are well-marked perpendicular grooves upon the anterior 

 surface of many of the plates The upper central plate is trian- 

 gular, from which fact the name Goniognatha has been applied to 

 the section I have called Orthalicinse. Cylindrella, Macrocera- 

 mus, Pineria, Partirfa, and some species of Bulimulus also have 

 an upper median triangular compartment to their jaw, but in their 

 case the jaw is in one single piece, with distant, delicate ribs, 

 running obliquely to the central line, some of the upper ones 

 meeting before reaching the lower margin of the jaw, thus leaving 

 a triangular space, not a separate piece. 



I have myself figured the jaw of 0. melanochilus, Yah, under 

 the name of 0. zebra (L. and Frw. Shells N. A., I., p. 215, fig. 367), 

 of gallina-sultana (Ann. N. Y. Lye. Nat. Hist., XI., pi. IV., fig. 

 E). The last named has also been figured by Troschel (Arch, 

 fiir Nat., 1849, pi. IV., iig. 3); the jaw of 0. iostomus is figured 

 by Crosse and Fischer (Moll. Mex. et Guat., pi. XIX., fig. 8), and 

 0. longus by the same authors (I., c. pi. XIX., fig. 1). I have 



