44 THE SHELL. 



d. Short, bucciniform. Buccinum (1, 2t). 



e. Fusiform, spindle-shaped. Fusus (xlvii, TO). 



/. Contabiilate, short, with shouldered whorls (xlvii, 82). 



g. Grlobular. JSTatica (Ixiii, 44). 



h. Gibbous. Whorls swelled beyond the normal contour 



of increase (usually on the aperture side ). Streptaxis. 

 i. Depressed, lenticular. Rotella (Ixxix, 95). 

 j. Discoidal. Daronia (Ixxix, 90). 

 k. Convolute ; aperture as long as the shell, nearly or 



quite concealing the spire. Cyprsea (Ixi, 96). 

 I. Trochiform, pyramidal, conical with a flat base. Trochus 



(Ixxx, 39). 

 m. Turbinated ; conical, with rounded base. Turbo 



(Ixxx, 29). 

 n. Cone-shaped, obconic. Conus (Iviii, 42). 

 0. Few-whorled. Helix haemastoma. 

 p. Many-whorled. Helix polj^gyrata. 

 q. Ear-shaped. Haliotis (Ixiii, 10). 



B. Scalariform, whorls not impinging. Scalaria (Ixvi, 42). 



C. Irregularly spiral, evolute. Siliquaria (Ixvii, 1^9). Yermetus 

 (Ixvii, 68). 



Z). Tabular. Dentalium, or tooth-shell. 



E. Shield-shaped. Umbrella (Ixxxix, 89 \ 



F. Boat-shaped, slipper-shaped. Navicella (Ixxviii, ^&). 

 Crepidula, (Ixv, 92). 



G. Conical or limpet-shaped. Patella (Ixxxiii, 26). 

 H. Multivalve and imbricated. Chiton (Ixxxvi, 85). 



The only symmetjHcal shells are those of Carinaria, Atlanta, 

 Dentalium and the limpets. 



The cavitj^ of the shell is a single conical or spiral chamber ; 

 no gastropod has a multilocular shell like the Nautilus, but 

 particular species, as we have seen, form spurious chambers by 

 partitioning off the whorls ; manj'' form such partitions as a 

 protection agaiiist the attacks of boring animals, or when the 

 upper part of the spire is destroyed. Some spiral shells are 

 complete tubes with the whorls separate or merely in contact, 

 as Scalaria ; but more commonly the inner side of the spiral is 

 formed more or less by the previous whorls. 



The axis of the shell, around which the whorls are coiled, is 

 sometimes open or hollow ; in which case the shell is said to be 

 perforated, or umbilicated, e. g. Solarium (Ixvi, 34). The perfo- 

 ration may be a mere chink, or fissure (7'ima), as in Lacuna 

 (Ixix, 32) ; or it may be fillfed up by a shelly deposit, as in many 

 Naticas (Ixiii, 45). In other shells, like the Triton, the whorls 

 are closely coiled, leaving only a pillar of shell, or 'columella, in 

 the centre : such shells are said to be imperforate. The name 



