CRUSTACEA. 
497 
TRIBE IV.-HETEROPA. 
Having fourteen feet constructed for swimming, or at least 
the last four.—The genera are, 20. Apseudes ; 21. lone. 
ORDER V.—ISOPODA. 
Head distinct; mandibles without palpi; three pairs of jaws, 
the lower one like two small feet, united at their base; or hav¬ 
ing a lip with palpi; body depressed, and divided into from 
three to seven segments; from ten to fourteen feet; tail with 
seven segments, or upwards ; having branchiae ; frequently co¬ 
vered with laminae; destitute of shell; with four antennae, and 
granulated eyes. 
Section I.—Aquatic a. 
With four antennae, the anterior with three or four joints; 
sometimes destitute of antennae ; lower appendages of the post¬ 
abdomen usually vascular, and without particular openings for 
the entrance of air. 
TRIBE I.-EPICARIDES. 
Body considerably depressed above, and concave below, tor 
containing the ova; without eyes, antennae, mandibles, and cau¬ 
dal fin.—It has one genus : 1. Bopyrus. , 
TRIBE II.-CYMOTHOADES. 
Four antennae and eyes, sometimes very indistinct; mandibles 
horny ; feet formed for walking, and also prehension ; a fin on 
each side of the posterior extremity of the body; post-abdomen 
consisting of from four to six segments.—Its genera are, 2. Cy- 
motboa; 3. iEga ; 4. Cirolana; 5. Eurydice; 6. Nelocira; 7. 
Limnoria; and, 8. Serolis. 
Genus 3. — ./EGA. — Leach. 
Generic Character. —The upper antennae with their two first 
joints broad and compressed; large, slightly convex eyes; tail 
with foliaceous appendages; abdominal joints with their sides 
imbricated. 
2 s 3 
