842 MANUAL OF THE MOLLUSCA. 
the centres. The buccal ganglia are situated considerably in 
front of the cephalic, and the pedal ganglia are far behind, so 
that the commissures which unite them are nearly parallel with 
the cesophagus. The branchial ganglia are at the posterior 
extremity of the body, as in the bivalves. The eyes are hour- 
glass shaped, and very perfectly organised; the auditory 
vesicles are placed behind, and connected with the cephalic 
ganglia, they each contain a round otolite, which sometimes 
seems to oscillate. (Huxley.) 
FAmiIty I.—FIROLIDA. 
Animal elongated, cylindrical, translucent, furnished with a 
ventral fin, and a tail-fin used in swimming; gill exposed on 
the posterior part of the back, or covered by a small hyaline 
shell. Mouth with a circular lip; lingual membrane with few 
rows of teeth; central teeth transversely elongated, with 3 
recurved cusps; laterals 3 on each side, the first a transverse 
plate with a hooked apex, 2 and 3 sickle-shaped.* 
FIROLA, Peron and Lesueur. 
Type, ¥. Coronata, Forsk. Mediterranean. 
Synonym, Pterotracheea, Forsk. 
Animal fusiform, elongated, with a long, slender, proboscidi- 
form head; fin narrowed at the base, furnished with a small 
sucker; tail elongated, keeled, sometimes pinnate; nucleus 
prominent; branchial processes numerous, conical, slender; 
tentacles 4, short and conical; eyes black and distinct, protected 
by a rudimentary eyelid; lingual ribbon oblong. The female 
firole haye a long moniliform oviduct. Anops Peronit, 
D’Orbigny, described and figured as haying no head (!), was 
probably a mutilated Firola. ‘‘ Such specimens are very 
common, and seem just as lively as the rest.”” (Huxley.) 
Distribution, 14 species. Atlantic, Mediterranean, Pacific. 
Sub-genus. Firoloides, Lesueur. (Cerophora, »)’Orbigny). F. 
Desmarestii, Les. Body cylindrical; head tapering, furnished 
with two slender tentacles; nucleus at the posterior extremity 
of the body, with or without small branchial filaments; egg- 
tube regularly annulated; tail-fin small and slender, ventral 
fin without a sucker. Distribution, 6 species. Atlantic ; Medi- 
terranean. 
* The genus Sagitta, Q. and G., sometimes referred to this family, is an articulate 
animal (Huxley.) 
