LABYRINTHUS. 175 
LABYRINTHUS. 
Labyrinthus, Beck, Index Moll. p. 33 (1838) ; Albers, Die Helic. ed. 1, p. 121, and ed. 2, p. 184; 
A. H. & A. Adams, Gen. Moll. ii. p. 200. 
Lyrostoma, Swainson, Malacol. p. 329 (1840). 
Shell depressed, narrowly umbilicated, of more or less deep brown colour. Aperture 
nearly horizontal, with a thickened, reflexed, continuous peristome, produced towards 
the centre of the shell into a more or less prolonged lobe, which descends into the 
umbilicus or terminates freely overtopping its hole; a large parietal fold on the wall 
of the aperture formed by the penultimate whorl, more or less flexuous; opposite to it 
there are on the under (basal) part of the peristome—first, one or two teeth or plaits, 
forming with it a more or less broad channel, and in addition, where the basal margin 
rises towards the periphery of the shell, another external basal tooth, often somewhat 
removed from the margin towards the interior, advancing in some species very near to 
the external end of the parietal fold, and so narrowing very much the lumen of the 
aperture. Sometimes a fourth little tooth, situated on the upper roof of the aperture, 
advances from above towards the same spot, as if completing the cruciform obstruction 
of it: but this little tooth is the most inconstant ; for instance, in L. hydeanus it may be 
present or absent. ‘The teeth or plaits of the basal margin are marked outside the 
aperture by corresponding grooves. ‘The whole apparatus is probably defensive, pre- 
CoMPARATIVE TABLE OF THE SPECIES OF LABYRINTHUS. 
Aperture Dentes 
Nomen. Figura. . . . Diam.} Alt. Patria. 
8 lobus cen- pars periphe-| marginis basalis . 
tralis. rica. interioris. exterior. 
mm. | mm. 
triplicatus, v. Mart. ...| convexo- rotundatus, j/rotundata. | unicus, remotus, 25-26| 12 | E. Costa Rica. 
depressa, brevis. parvus, compressus, 
obtuse simplex. simplex. 
angulata. . 
quadridentatus, Brod. | trochiformis, ” | - duo, prior] subremotus, 20 11 | S.W. Costa Rica. 
distincte | obtusus triangularis, 
angulata. humilis, compressus. 
| secundus 
| transversus. 
uneigerus, Peé7iz......... depresse » obtuse subcompres- | remotus, 29-36 | 133 | Isthmus of 
lenticularis, angulata. sus, trans- | acutus, Panama. 
acute cari- versus. curvatus. 
nata. 
annuliferus, Pfr. ...... lenticularis, | subelongatus, | rostrata. subdepressus,| magnus,com-| 34 13 | Panama. 
acute albo-| angustior, transversus.| pressus, ro- 
carinata. descendens. tundatus. 
plicatus, Born ......... sublenticu- | subelongatus,| rostrata et | mediocris, magnus, sub- | 42-51 | 17-22 | N. Panama. 
laris, supra} sat angus-| paulum depressus. quadratus, 
magis con-| tus,in um-/ emarginata. marginalis. 
véxa, acute} bilicum 
carinata. descendens. 
