■24 
FORMS OF SHELL IN UNIVALVES. 
aperture is on your right hand tlie shell is dextral, if on your left, 
sinistrul, as shown in the foregoing figures. 
The length of the tube, its shape, and its closer or more open 
mode of convolution, gives rise to a great variety of forms amongst 
the different .species, the principal of which are 
Elongate, Terete, or Subulate, when the shell has 
the spire greatly produced and pointed, as in 
Ili'U.r acuta j^lulh, CwciUoide^ acicula, (Mull.), 
lialca peri'evMi (L.), etc. 
Fig. 2D. — Example : Helix acuta Miiller, Point Scarlet, near Castletown, Isle of Man, 
collected by Mr. A. Taylor. 
Turreteu, when the shell is elongate, but the upper 
portion (jf the whorls are shouldered or angulated, 
as in L'niuuva truncatula (Miilh). 
Fig. 21. — Example : Limnwa truncatula var. turrita Clessin, ditch, Ilicriey, near 
Bradford, Yorks. 
CvLiNDurc.VL, when the shell is cylindrically elon- 
gated, as ill Pupa muscorum (L.), Vertigo eden- 
tula (Drap.), etc. 
Fig. 22. — Example : Puf>a inuscoruiu var. clonc^ata Clessin x 3, rcjectamcmla of River 
Stour, Sandwicli, Kent, collected by .\ir. S. C. Cockerell. 
Fusiform, or Si’inole-.sii.vi'ED, when the shell is 
swollen in the middle and tapering at each end, 
as in Auxa trident (Fult.), C/ausi/ia lamiuata 
(iMont.), etc. 
Fig. 23— Example: Azcca tridcns yixx. noulctiana Dupuy X 3, Lewes, Sussex, collected 
by Mr. T. S. Hillman. 
Tufhun AT i'R), when the shell is of a conical shape, 
with a. rounded base, as in Liiuihca sfa^f/udis 
(Einiie), llpf/ini/a teutacuUda (L.), Viripara 
rii'ijiara (L.), etc. 
Fk;. L'L— E.xainpli; : Hytkinia ti iilaculata (I,.) X 2, River Lc-.v, C'lnniiroril, Essex, colleclvtl 
b}' l)r. R. F. Scharfl', 15. Sc. 
CoNTABULATE, ivlieii the shell is short, with 
shouldered or angulated whorls, as in 
Lnnna’a rfaguahr var. hodaiiiiea IMdler, 
Plntra fiDitinal!^ v. iuttata Moij., etc. 
Fiii. 2.3.— Example : Linuuca stai^nalis \:xx. bodainica Miller, Roden See, Swit/crland, 
collected by Herr Schenk. 
