The; Genus Gyrotoma 9 



they appear to run decidedly larger and this is not to be explained by the 

 size of the aperture. The nucleus of all except pyramidatiim is quite close 

 to the left margin and near the base. 



A few opercula have been illustrated, but without any intention of ac- 

 centing differences. ]\Iany of the dift'erences are possibly due to variations 

 in the erosion to which this feature is subjected in strong currents. The 

 opercula of quite young Gyrotomae are very nearly uniform. 



Genus Gyrotoma Shuttleworth 



Schizostoma Lea, (non Bronn, i8.'?.s), Proc. Amer. Phil. Soc. II, 184.1, P- 242 r 

 Trans. Amer. Phil. Soc, IX, 1844. p. 26; X, 1848. pp. 67. 0.1 ; I. n. s., 18.S2. p. 2Q5 ; 

 Proc. Acad. Nat. Sci.. Phila., XII. i860, p. 186; Journ. Acad. Nat. Sci., Pliila., V. n. s., 

 icS62, pp. 218, 24.3. 24^, 246; VI, 1866, p. i!^2; Obs. Gen. Unio, IV, 1848. pp. 26. 67, 93; 

 V, i8s2, p. 51 ; IX, 186.3, pp. 40. 65, 67. 68; XI, 1867, p. 108; Tryon, Amer. Journ. Con- 

 chol., I, 1865, pp. 114-116, 131; II, 1866, p. 134; Lewis, Amer. Tourn. Conchol., V, i86q- 

 70, p. 168; Tryon, Monog. Strepom., 1873, PP- xxiii-xxvii. xxxiii. xxxv. 

 xxxix, xlvi, .3.S1: Hinkley, Nautilus. XVIII, IQ04. p. 40. 4i. 



Gyrotoma Shuttleworth, Mittheil. der Nat.-forsch. Gesellsch. in Bern., July 

 ,22, 1845, p. 88; H. & A. Adams, Genera, I, 1854, p. 305; Gray, Guide td Mollusca, I, 

 1857, p. 103 ; Chenu, Man. de Conchyl., I, 1859, p. 293 ; Anthony, Proc. Acad. Nat. Sci., 

 Phila., XII, i860, p. 53 ; Binney, Check List, i860 ; Brot, List, 1862, p. 27 ; Tryon, Monog. 

 Strepom., 1873, pp. xv, xviii, xxiii, xxiv-xxvii ; Paetel, Cat., 1888, p. 361 ; Pilsbry, Proc. 

 Acad. Nat. Sci., Phila., 1896, p. 497; Hannibal, Proc. Malacol. Soc, X, 1912, p. 179. 



Schizochilus Lea, (non Gray, 1850), Trans. Amer. Phil. Soc, X, n. s., 1852, p. 

 295; Obs. Gen. Unio, V, 1852, p. 51 ; IX, 1863, p. 67; Proc Acad. Nat. Sci., Phila., XII, 

 i860, p. 186; Journ. Acad. Nat. Sci., Phila., V, n. s., 1862, p. 245; Tryon. Monog. 

 Strepom., 1873, pp. xxiv, xxxiii. 



Melatoma Anthony, Gray, Proc. Zool. Soc. of London, 1847, p. 153; Woodward, 

 Manual, 1851, p. 131; Reeve, Conch. Icon., i860. 



Apella Mighels, MS., i860. 



"Shell turreted ; columella incurved, thickened above by an intermarginal 

 callus; aperture oval, somewhat spread out (effuse) at the base; lip simple, 

 sharp, with a narrow fissure, deeply notched. 



"Animal. ; operculum corneous, spiral." — Shuttleworth. 



Group oe Gyrotoma pyramidatum 



Rather heavy, pyramidal especially in the young, sometimes nodose, 

 smooth to striate; fissure shallow, oblique, not exceeding 8 mm. in depth; 

 girdle not always conspicuous ; aperture ovate ; sinus not pronounced ; bands 

 usually four and of equal width. 



Gyrotoma pyramidatum Shuttleworth 

 PI. I, figs. I, 2, and 3 



Gyrotoma pyraviidata Shuttleworth, Mittheilungen der Naturforschenden Gesell- 

 shaft in Bern, No. 50, July 22, 1845, p. 88; H. & A. Adams, Genera, I, 1858, p. 305; 

 Binney, Check List, i860. No. 329; Brot, List, 1862, p. 27; Paetel, Cat., 1888, p. 361. 



Gyrotoma conica Shutt. (?), Troschel, Gebiss der Schnecken, I, 1857, p. in, pi. 8, 

 fig. 12; Brot, List, 1862, p. 27; Tryon, Monog. Strepom., 1873, P- 380. 



