ORTHALICUS. 407 



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 lg 



be said to be composite, as the amalga- 

 mation 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 



' i Jaw of O. undatus. 



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 triangular, from which fact the name Goniognatha 

 has been applied to the section. Cylindrella, Macroceramus, Pineria, Partula, 

 and some species of Bulimulus also have an upper median triangular compart- 

 ment 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, Val., under the name of 

 0. zebra (L. and Fr.-W. 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, fur Nat., !849, PI. IV. Fig. 3) ; the jaw of 0. iosto- 

 mus is figure by Crosse and Fischer (Moll. Mex. et. Guat., PI. XIX. Fig. 8), 

 and O. longus by the same authors (I. c, PI. XIX. Fig. 1). I have also exam- 

 ined the jaw of O. obductus, Shuttl. (Ann. Lye. N. H. of N. Y., XI. p. 37). 

 All these species have the same composite type of jaw. 



The lingual dentition of Orthalicus undatus is so nearly similar to that of 

 Liguus fasciatus, that I merely compare it with the description given above of 

 that species. The membrane is broad (see PI. XVI. Fig. M). In 0. undatus 

 the central tooth (PI. X. Fig. H) is broader in proportion to its length ; the 

 base of attachment is less expanded at the upper margin, and very much 

 less so at its lower margin, and the sides are not incurved ; the cusp is stouter, 

 longer, reaching the lower edge of the base of attachment, and it has subobso- 

 lete but distinctly marked side cusps ; the cutting edge is much more ex- 

 panded, overlapping the next row of teeth. The first marginals difTer from 

 those of L. fasciatus in having a less developed cutting edge, the outer mar- 

 ginals have the side spurs to their cusps much more developed, and even the 

 cutting edge is trilobed. The extreme marginals are not so small. There are 

 about 53 — r — 53 teeth on one part of one membrane ; a wide part of another 

 membrane had 106 — 1 — 106. 



