842 EXPLANATION OF PLATES. 



Fig. 4. Area tortuosa L., p. 733. 



Fig. 5. Shell of Trigonia pectinata LAM., p. 734. From the inside, to 

 shew the hinge (cardo). 



Fig. 6. Venus Dione L., Cytherea Dione LAM., p. 742. The shell is 

 placed in the position according to which LINNAEUS has described 

 it (see the note, p. 683), namely, with the point, A, downwards; 

 ihefissura, b, forwards ; the lunula, a, backwards. 



Fig. 7. Venus (Cytherea) erycina LAM. Right valve from within. A, the 

 point; a, lunular cavity; b, fissure; c, hinge; d, impression of 

 the anterior ; e, of the posterior adductor muscle ; f, impression 

 of the mantle ; g, g, inferior margin of the shell. In this figure 

 the shell is placed in its natural position. On the left side the 

 fore end is placed, which the animal, when moving, directs for- 

 wards. 



Figs. 8 11. Examples of univalve shells or cochleae, p. 683. 



Fig. 8. Shell of Purpura Concholepas, p. 807. 



Fig. 9. Shell of Patella, p. 790 ; Patella umbella GM. 



Fig. 10. Shell of Scalaria imperialis, p. 798. 



Fig. 11. Shell of Bulimus citrinus BRUG., p. 814. Example of a Cochlea 

 sinistra, see p. 684. 



PLATE XIV. MOLLUSCS. 



Fig. 1. Shell of Oliva erythrostoma LAM., p. 810 ; example of an invo- 

 lute shell, p. 683. A, the aperture ; a, external margin ; b, in- 

 ternal margin. 



Fig. 2. Shell of Nautilus Pompilius L., divided in the midplane, p. 825, 

 an example of a shell rolled upon itself, and at the same time 

 many-chambered (cochlea revoluta, polythalamia) pp. 683, 684; 

 A, A, the last chamber, or cavity, in which the animal lies ; a, a, a, 

 the siphon which traverses the successive chambers. 



Fig. 3. A cover (Opercutwn) of Turbo, from the inside ; see p. 684. 



Fig. 4. Salpa (runcinata .?) p. 699. Of the natural size, from a specimen 

 presented to me by Prof. Y. BENEDEN. A, the animal seen from 

 the surface which is commonly turned upwards, according to 

 ESCHRICHT the ventral surface. Here the muscular belts extend 

 throughout; B, the animal seen from the opposite side, where 

 the muscular belts are interrupted ; a, (in fig. A) the fissured 

 aperture which the animal turns forwards ; b, the posterior 

 aperture ; c, the so-named nucleus, or the collection of the vis- 

 cera ; d, the salpa chain in process of development ; f, g, muscular 



