P^CILOPODA. 147 



least half the length of the body. This subdivision will com- 

 prise two genera of MuUer. 



Argulus, Mull. 



This genus was at first designated under the name of Ozolus, and 

 but very imperfectly described. Jurine, Jun. has since studied its 

 type with the most scrupulous attention, followed it throughout all 

 its changes of age, and produced a perfect and complete monograph 

 of it. He has restored to the genus the original name given by 

 Miiller. 



The Arguli are furnished with an oval shield, posteriorly emargi- 

 nated, covering the body, the posterior extremity of the abdomen 

 excepted, and bearing on a mediate, triangular space distinguished 

 by the name of clypeus, two eyes, four very small, almost cylindri- 

 cal antennae placed in front, the superior of which, shorter and tri- 

 articulated, have a stout, edentated and recurved hook at their basej 

 and the inferior quadriarticulated, with a small tooth on the first 

 joint. The siphon is directed forwards. There are twelve feet. 

 The two first terminate in a transversely annulated disk, striated 

 and edentated along the margin, and presenting internally a sort of 

 rosette formed by the muscles, and apparently acting in the manner 

 of a cup or sucker. Those of the second pair are prehensile, the 

 thighs large and spinous, and the tarsi composed of three joints, the 

 last of which is provided with two hooks. The remaining feet are 

 terminated by a fin formed of two elongated pinnulae, whose edges 

 are fringed with bearded threads: the two first of the latter, or those 

 of the third pair, including the four that precede them, have an ad- 

 ditional but recurved toe. The two last are annexed to that portion 

 of the body which projects posteriorly from the shell, or the tail. 

 The female has but a single oviduct covered by two small feet situ- 

 ated behind the two palettes. The organ which is considered as the 

 penis of the male, is placed at the internal extremity of the preceding 

 joint of the same feet near the origin of the two toes. On the same 

 joint of the two preceding feet, and facing these organs of copula- 

 tion, is a vesicle presumed to be seminal. The abdomen, by which 

 we mean that part of the body which extends posteriorly from the 

 ambulatory feet, the rostrum, and a tubercle containing the heart, 

 is entirely free, without distinct articulations, and terminates directly 

 after the last feet behind, by a sort of tail, in the form of a rounded 

 lamina, deeply emarginated or bilobate, and without terminal hairs: 

 it is a species of fin. The body is so transparent that the heart may 

 be distinguished through its parietes. It is situated behind the 

 base of the siphon, lodged in a solid tubercle, semi-diaphanous and 



