EXPLANATION OF PLATE XVIII. 
FiGcureE 89.—Branchiobdella Ravenelii, (p. 624 ;) dorsal view, natural size 
90.—Malacobdella obesa, (p. 625 ;) dorsal view. 
91.—Pontobdella rapax, (p. 625;) dorsal view. 
92.—Phascolosoma cxementarium, (p. 627 ;) lateral view. 
93.—P. Gouldii, (p. 627 ;) lateral view, reduced one-half. 
94.—Pontonema marinum, (p. 634;) female, lateral view, enlarged 15 diam- 
eters; 0, egos; v, genital orifice. 
(Figure 94 was drawn from a living specimen, by A. E. Verrill; all the ethers were drawn from pre- 
Served specimens, by J. H. Emerton.) 
