EXPLANATION OF PLATES. 843 



belts ; k, the gill ; I, the heart r, dorsal folds (endostyle ?) ; t, 

 languet ; b, (in B) the cerebral ganglion. 



Fig. 5. Ascidia (Cynthia) Momus, p. 707; after SAVIGNY Memoires, n. 

 PL vi. fig. 1. A, respiratory aperture ; B, cloacal aperture j c,c,c, 

 outer covering, of which one half is removed in order to shew 

 the internal envelop d (the mantle) ; e, muscular fibres on the 

 mantle. 



Figs. 6, 7. Fig. 6. Lingula anatina LAM., p. 721 ; after CuviERAnn. du 

 Mus. i. fig. 6. The animal in its shell with the peduncle B. 



Fig. 7. The animal removed from the shell, one of the laminae 

 of the mantle thrown upwards ; a, the cerebral ganglion, accord- 

 ing to CUVJER b, mouth ; c, c, the two arms ; d, d, d, d, pectinated 

 gill-folds on the mantle. 



Fig. 8. The animal of an Anodonta in the shell, of which the right valve 

 is removed, as an example of Lamellibranchiates, pp. 723, 724 ; 

 comp. PI. 15, fig. 1 j a, shell (left valve from the inside) ; b } b, 

 the two laminae of the mantle ; c, c, outermost gills ; d, e, inner 

 gills j g, the flat ventral disc projecting between the gills ; * ten- 

 tacles round the mouth, those of the right side alone are seen ; 

 t mouth ; A, anterior adductor muscle ; b', b', the posterior 

 border of the mantle beset with fringe-like appendages. 



PLATE XV. MOLLUSCS. 



Fig. 1. A transverse section of Anodonta anatina, schematic after NEU- 

 WYLER, Neue DenJcschr. der ally. Schweizer. Gesellsch. fur die 

 gesammten Naturwissenschaften, Bd. vi. 1 842, Tab. 1 ; a, a, b } b f 

 and g, as in fig. 8 of the preceding plate ; c, external laminae of 

 the outer gills with the dorsal side attached to the mantle ; d, 

 internal lamina of the outer gill ; e, external ; f, internal lamina 

 of the inner gill ; h, heart, traversed in the middle by the 

 rectum. 



Fig. 2. Solen legumen L., p. 754 ; after POM Test. utr. Sicil. I. Tab. XL 

 fig. 15 ; A, the foot projecting at the anterior extremity of the 

 shell ; B, c, the two tubes (tracheae) coming into view from the 

 shell behind. 



Fig. 3. Clio borealis GMEL., p. 775 ; after ESCHRICHT Anat. Unters. 

 Tab. i. fig. 3 ; the animal is represented from the ventral surface ; 

 a, a, fin-like appendages ; &, b, conical appendages ; c, c, tentacles 

 of the head ; d, everted penis with a vesicle d' at the base. 



