MOLLUSCA. 785 
The heart lies in these molluscs in the middle of the body on the 
dorsal surface, and receives the blood from the gills placed on each 
side. Mitne Epwarps unites this family with the preceding and 
the next following into a common order under the name of Opis- 
thobranchia. This family approaches, however, very near to the 
preceding, and especially to the genera Doris and T'ritonia. 
Phyllidia Cuv. Head with four tentacles, the two superior 
retractile within a cavity. Anus in posterior and middle part of 
back. 
Comp. Cuvier Ann. du Mus. v. pp. 266—276, Pl. xvirt. Mollusg., Mém. 
Vill. 
Sp. Phyllidia trilineata Cuv., Phyll. varicosa Lam., Cuv. 1. ¢. figs. 1—6, 
Buainv. Malac, Pl. 47, fig. 1; in the Indian and Red Seas, as also Phyyl- 
lidia pustulosa Cuv. ibid. fig, 8, LevoKart in Atlas zw der Reize von 
E. Rurpre., Wirbellose Thiere des rothen Meeres, p. 36, Tab. XI. fig. 1. 
Pleurophyllidia Mucx., Diphyllidia Cuv., Armina RAFIn. (on 
the authority of CANTRAINE), Linguella BLAInv. Head with two 
tentacles placed towards the back at the anterior margin of mantle. 
Frontal veil with angle produced on each side. Vent in right side, 
behind genital foramen. Mantle acuminate posteriorly. 
Sp. Plewrophyllidia lineata, Diphyll. lineata Orro, Nov. Act. Acad. Ces. Nat. 
Cur. xvul.; DELLE CHIAJE Memorie, I. p. 128, Tab. 10, figs. 12—20; 
MEcKEL Archiv f.d. Physiol. vit. 1823, Taf. 1. figs. [—7, s. 1g0—207, 
CANTRAINE Malac. mediterr. p. 63, Pl. 2, fig. 4, inthe Mediter. and accord- 
ing to Lovén in the North Sea also. Diphyll. verrucosa CantTR. ibid. fig. 3. 
Comp. Diphyll. ocellata Dusu., R. Ani., éd. ill., Moll. Pl. 31, fig. 2. (The 
specimen from the collection of BRUGMANS, on which CuviErR founded this 
genus, now in the Rijks Museum of Leyden, Diphyll, Brugmansii Cov., is of 
one colour, pale and with a smooth mantle.) 
Family VI. Pleurobranchiata. Marine gasteropods hermaphro- 
dite, naked or furnished with a small internal shell, more rarely 
external. Branchiz composed of divided lamin resembling leaves 
pinnatifid or supradecomposed, on one side only, where are also the 
vent and orifices of generation, mostly situated on the right side or 
backwards on the back, more or less covered by the mantle. 
This family, named by Cuvier T'ectibranches, which was trans- 
lated by many writers Pomatobranchia, by MENKE Crypsibranchia, 
has no greater claim to this name, or even less than many other 
divisions of molluscs. We adopt therefore the name of Plewrobran- 
chiata instead of the sesqguipedale of BLAINVILLE Monopleurobranchiata 
Tas Ts 50 
