ORDER AMPHIPODA. 207 



The second, Gammarin^, Latr., have always four an- 

 tennEe ; the body is invested with coriaceous elastic tegu- 

 ments, and generally compressed and arched ; the posterior 

 extremity of the tail is without fins ; its appendages are in 

 the form of cylindrical or conical styles ; two at least of their 

 four anterior feet are most frequently terminated in a pincer. 



The vesicular pouches, in those in which they have been 

 observed, are situated at the external base of the feet, be- 

 ginning from the second pair, and accompanied by a small 

 lamina. The pectoral scales enclosing the eggs are six in 

 number. 



Sometimes the four antennae, although of different propor- 

 tions in many, have essentially the same form and the same 

 uses. The inferior do not resemble feet, nor perform their 

 functions- 

 One subgenus, which we have established under the deno- 

 mination of 



Tone, 



After a figure of Montagu's {Oniscus thoracicus, Linn. Trans. 

 IX. iii. 3, 4.) presents us with very peculiar characters, and 

 which remove it from all the others of the same order. The 

 body is composed of about fifteen articulations, but distin- 

 guished only by lateral incisions, in the form of teeth ; the 

 four antennae are very short ; the external, longer than the 

 two others, are alone visible, when the animal is observed at 

 the back ; the first two segments of the body are each provided, 

 in the female, with two elongated cirri, fleshy, flatted, and 

 similar to oars ; the feet are very short, concealed under the 

 body, and hooked ; the last six segments are provided with 

 lateral appendages, fleshy, elongated, fasciculated, simple in 

 the male, branchy in the other sex. We also see at the pos- 

 terior extremity of the body, six other simple, curved ap- 

 pendages, two of which are larger than the others ; the abdo- 



