21 



beneath, and are the only visible portions of the rndimentary ninth 

 segment. The anal opening is a narrow slit between the bases of the 

 terminal spines. The animal breathes by means of two large valvular 

 spiracles placed close together at the tip of the eighth segment. Closed 

 or rudimentary stigmata also occur on the mesothorax and on abdom- 

 inal segments one to seven inclusive.* 



The habits of the larva do not differ from those of the imago. Both 

 live in shallow water or under partly submerged stones at the margins 

 of streams. In City Canyon, Utah, larvae and imago were found to- 

 gether clinging to floating sticks and willow catkins caught in an eddy 

 of the stream. They were feeding apparently upon the drowned in- 

 sects brought down by the water and lodged in the debris. When dis- 

 turbed, they released their hold ui^on the floating fragments, and with 

 outstretched legs sank helplessly to the bottom or were caught and 

 borne away by the current. Although rather sluggish, they can crawl 

 about actively under water, and soon regain the shore if carried be- 

 yond their depth. 



The larva of Amphizoa presents affinities with widely separate 

 groups of the Adephagons series of Coleoptera. The explanate, lobed 

 margins of the dorsal shields and the broadly fusiform shape of the 

 body exactly reproduce the general appearance of the larva of Cychrus. 

 The number of the stigmata, structure of the mandibles, and form of 

 the buccal cavity, together with its ambulatory habits, are likewise 

 characters which tend to connect it with the Carabidae, but the eight- 

 jointed abdomen forbids its entrance into this family. On the other 

 hand, the non-suctorial jaws effectively separate Amphizoa from the 

 Dytiscidae, although it has very many structural affinities with the 

 water beetles, particularly with the tribe ColymhiUni^ for example in 

 the position and structure of the antenn<e, the form of the maxillae and 

 the lower lip, the terminal spiracles of the eighth segment and the cerci 

 arising from a concealed ninth segment, the anal segment being also 

 suppressed. Finally, with the European genus Pelobius, Amphizoa 

 shares nearly all the distinctively Dytiscid characters which this genus 

 possess. The larva of Pelobius is wholly aquatic and breathes by 

 branchiae, but the obsolete stigmata are indicated precisely as in Am- 

 pliizoa, with the exception of the last pair, which in Amphizoa are 

 open spiracles, but in Pelobius are suppressed; the terminal eighth 

 segment being prolonged in a swimming stylet. The larva in both 

 genera has non-suctorial jaws. Schioedte's figure of the new-born larva 

 of Pelobius, t with its enormously disproportionate, carapace-like head 

 and general crustacean resemblance, suggests the suspicion that Am- 



* A full description of the larvae of Amphizoa has been presented before the Ento- 

 mological Society of Washington at its meeting held May 4, 1892, and will be pub- 

 lished in vol. II, No. 3, of the Proceedings. 



t Kroyer's Naturh. Tidsskrift, vol. viii, 1872, pi. v. Fig. 1. 



