PLEUROBRANCHUS. 191 
imens either living or alcoholic. Without these data, which are 
supplied in very few except the European species, nothing can be 
done toward this end. No monograph of the family has hitherto 
been published. The shells of a few species have been figured in 
the Conchologia Iconica; and Vayssicre and Bergh have supplied 
admirable anatomical details of the structure of the European 
| species. 
Synopsis of Genera and Subgenera. 
I. Mantle with the edge free and overhanging on all sides; rhin- 
ophores close together, inserted below anterior edge of mantle 
on a frontal veil (Plewrobranchine). 
a. Shell wholly immersed in the closed mantle. 
b. Penis or its foramen close to female orifice, 
PLEUROBRANCHUS, p. 191. 
bb. Penis or penial foramen some distance in front of 
female orifice, mantle generally notched in front or 
behind, Oscantus, p. 212. 
aa. Shell partly exposed by an orifice in the mantle, 
GYMNOTOPLAX, p. 210. 
II. Mantle passing without boundary into the broad anterior veil, 
the rhinophores far apart, inserted on the surface of united 
mantle and veil; no shell, (Plewrobrancheine). 
a. Right, left and posterior borders of mantle freely project- 
ing, separated from the foot by a groove, KoonsiA, 
pa 22h: 
aa. Posterior and left borders of mantle passing directly into 
the integument of the foot, not free or projecting, 
PLEUROBRANCHAA, p. 223. 
b. Buccal rostrum when projected very large; veil of 
moderate size Pleurobranchea. 
bb. Buccal rostrum slender; body orbicular, the veil 
very large, crescentic Euselenops. 
III. Genus HaLiorineELua (p. 209) is not included in the above 
synopsis, as its characters are unknown. The shell is similar 
to that of Pleurobranchus. 
Genus PLEUROBRANCHUS Cuvier, 1804. 
Pleurobranchus Cuv., Ann. du Mus. d’Hist. Nat., v, p. 275.— 
Berthella Buatnvitux, Dict. Sci. Nat., xxxxi, p. 370, 1826, for 
B. porosa=plumula.— Cleantus Lracu, Synops. Moll. Gt. Brit., p. 
4 
