410 



CRUSTACEOLOGY. 



Family I. Nymphonides. 



Polpi two in number. 

 Genus I. Nymphon. Mandibules armed with a for- 



ceps. 



Family II. Phoxichilides. 



No palpi. 

 Genus II. Phoxichilus. Mandibules terminated by 

 a simple bent nail. 



TRIBE II. AGNATHONIA. 



Eyes two in number. Ovifera none? Mandibules 

 none. 



Family III. Pycnogonumides. 



No mandibules. No ovifera ? 

 Genus III. Pycnogonum. Mouth furnished with a 

 simple tube. 



ORDER II. ELEUTEROSOMA. 



Head connected with the thorax, which is generally 

 distinct from the abdomen. Thorax feet bearing. 

 Feet six or eight in number. 



TRIBE I. HEXAPODA.* 

 Feet six in number. 

 Family IV. Astomides. 



Feet six in number. 



A. Palpi and rostrum very conspicuous. 



Genus IV. Caris. Body consisting of one coria- 

 ceous piece, which is much depressed, and nearly or- 

 bicular. 



Genus V. Leptus. Body soft and eval. 



B. Palpi a?id rostrum obscure. 

 Genus VI. Astoma. Feet very short. 



TRIBE II. OCTOPODA. 



Feet eight in number. 

 A. Abdomen sessile, without any appearance of rings ; 

 Mouth generally produced into a rostrum or haustel- 

 lum. 



Family V. Hydrachnides. 



Feet formed for swimming. 



Genus. VII. Limnochares. Rostrum scarcely pro- 

 jecting. 



Palpi without appendages. 



Body depressed. 



Mandibules none. 



Genus VIII. Hydrachna. Mandibules none. 



Rostrum conic, projecting, the points sharp. 



Palpi projecting, the apex with a moveable appen- 

 dage. 



Genus IX. Elais. Mandibules depressed, the points 

 armed with a nail. 



Family VI. Ricinides. 



Feet not formed for swimming; no mandibules; 

 rostrum shaped like a bird's beak, or hunter's horn. 



I. Eyes distinct. Body very soft and thick ; the 

 dorsal Skin not coriaceous. 



* Palpi obscure, not projecting. 



Genus X. Sarcoptes. 



** Palpi more or less distinct. 



Genus XI. Bdella. Palpi slender, filiform, long, 

 and elbowed, the extremity armed with hairs. 



Eyes four. 



Posterior feet very long. 



Genus XII. Smaris. Palpi slender, straight, and 

 filiform, a little longer than the rostrum, without any 

 setae at the extremity. 



Eyes two. 



Anterior feet very long. 



Genus XIII. Cheyletus. Palpi very thick, resem- 

 bling arms. 



II. Eyes indistinct : Body with a covering, partly 

 membranaceous, partly coriaceous. 



* Palpi and rostrum obscure. 

 Genus XIV. Uropoda. Feet very short; anus with 

 a filament, by which it attaches itself to insects. 

 ** Palpi and rostrum distinct. 

 Genus XV. Argas. Palpi short, conic, and free, 

 not covering the rostrum. 



Genus XVI. Ixodes. Palpi short and depressed, 

 embracing the rostrum, and sheathing it. 



Family VII. Acarides. 



Feet not formed for swimming ; with mandibules. 



I. Palpi very short, and not projecting. 



Genus XVII. Acarus. Body very soft. Mouth 

 naked. 



Genus XVIII. Oribita. Body covered wirh one 

 coriaceous plate. The rostrum covering the parts of 

 the mouth. 



II. Palpi projecting. 



* No hook or moveable appendage at the extremity of 

 the palpi. 



Genus XIX. Gamasus. 



** An hook or moveable appendage at the apex of the 

 palpi. 



Genus XX. Erythr^eus. Body not divided. Eyes 

 sessile. 



Genus XXI. Trombidium. Body divided into two 

 parts ; the anterior division bearing the eyes, the mouth, 

 and two first pairs of feet. 



Eyes pedunculated. 



B. Abdomen fixed or sessile, sometimes ringed, 

 Mouth not prolonged into an haustellum or rostrum. 



Family VIII. Phalangides. 



Mandibules armed at their points with forceps ; abdo- 

 men generally sessile ; anus without tubercles of nipples. 



I. Eyes not placed on a peduncle or tubercle. 

 Genus XXII. Siro. Mouth naked : Mandibules ve- 

 ry long. 



Genus XXIII. Trogulus. Mouth situated in a ca- 

 vity, under the anterior part of the thorax ; mandibules 

 short. 



II. Eyes placed on a common tubercle. 



Genus XXIV. Phalangium. Eyes two. Palpi ter- 

 minated by a hook. Body orbicular. 



Genus XXV. Galeodes. Eyes four; palpi with no 

 hook ; body elongated. 



Arsihuii 

 des. 



* In the Appendix we have added two other genera to this tribe, \i», Nyeteridia, which Latreille places with the Insecta, and a 

 Hew genus, named by Dr Leach Ocypete. 



