ORDER TECTIBRANCHIATA. 47 
rate from the animal, took it for a shell, and made a genus of 
it, to which he gave his own name. He even went so far as 
to describe its pretended habits. Draparnaud was the first 
who perceived this mixture of error and fraud. 
Bulla ampulla, L., Martini. I. xxii. 20. 204; Cuv. Ann. du 
Mus. XVI.i. The shell oval, thick, clouded with grey and 
brown; the stomach furnished with three black, very convex, 
rhomboidal pieces. 
Bulla hydatis, L., Chemn. IX. exviii. 1019; Cuv. Ann. du 
Mus. xvi. 1. Shell round, thin, and semi-diaphanous, the last 
whorl, and consequently the aperture, higher than the spire ; 
three small scutelliform pieces in the gizzard. 
Add Bulla naucum, Bulla physis, &c. 
We reserve the name of AKERA, properly so called, (Dort- 
DIUM, Meck.; LOBARIA, Blainv.) for those species which 
have no shell whatever, or only a vestige of one behind, 
although their mantle has its external form. 
A small species, Bulla carnosa, Cuv. Ann. du Mus. xvi. 1; 
Meck. Anat. Compar. IT. vii. 1. 3; Blainv. Malac. pl. xlv. f. 
3; 1s found in the Mediterranean. ‘The stomach is no more 
armed than the mantle; its fleshy cesophagus is extremely 
thick. 
We also find in the same sea a tuberculous species, Dor?- 
dium Meckelii, Delle Chiaie Memor. pl. x. f. 1—5. 
GASTROPTERON, Meck., 
Appears to be an akera, the margin of whose foot is developed 
into broad wings, serving for swimming, which it performs on 
its back. It has no shell nor stony armature to the stomach. 
A slight fold of the skin is the only vestige of a branchial 
operculum that is visible. 
The known species is also from the Mediterranean, Gas- 
tropteron Meckelit, Kosse. Diss. de pteropodum ordine. Hale. 
1813, f. 11—13; and Blainv. Malacol. pl. xv. f.5; or Clio 
