. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. ORTIIALICUS/ 407 lower portion positively detached and free, imbricated one upon another. The jaw may in one sense be said to be in a sin|rlc piece, as argued recently by Messrs. Fischer and Crosse (Moll. Mox. ct Gnat.), but with c(jual correctness it may surely ^_^^^ 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 ' j^^ ^^ ^ vnda
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. ORTIIALICUS/ 407 lower portion positively detached and free, imbricated one upon another. The jaw may in one sense be said to be in a sin|rlc piece, as argued recently by Messrs. Fischer and Crosse (Moll. Mox. ct Gnat.), but with c(jual correctness it may surely ^_^^^ 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 ' j^^ ^^ ^ vndatus. apparently lying upon the adjoining ones, which are broad and extend from the upper to the lower margin of the jaw. Tlie 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. Cyllndrella^ Macroceramus, Pineria, Parlula^ and some species of BuUmulus 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 Shells N. A., I. p. 215, Fig. 3G7), of gallina-sultana (Ann. N. Y. Lye. Nat. Hist, XI. PL IV. Fig. E). The last-named has also been figured by Troschel (Arch, fiir Nat., 1849, 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 0. ohductus, Shuttl. (Ann. Lye. N. H. of N. Y., XL p. 37). All these species have the same composite type of jaw. The lingual dentition of Orthalicus
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