220 [October, 1S83. 



Tlie Pelagic Hemipteva, which, indeed, are the only insects having a truly 

 oceanic habitat, forming the subject of this Monograph, consist, as far as at present 

 known, of but few species, and are referable to at most two or three genei'a, of 

 which only two — Halulates, Eechscholtz, and Halobatodes, F. B. White, are here 

 adverted to. These very remarkable insects, which are allied to the common aquatic 

 genus Oerris, are quite destitute of elytra and wings, have a thorax often occupying 

 three-fifths of the entire length of the body and very broad (the latter indicating 

 great development of the muscles governing the necessarily excessive action of the 

 legs) ; an extremely small, disproportionate abdomen (also advantageov;s to the con- 

 ditions of their life) ; and an excessive length of the second and third pairs of 

 filiform legs, this structure, as in Oerris, being admirably adapted for coursing over 

 the surface of water. That some of the species can dive has been observed ; it is 

 very probable that all do so on occasion (as we have often seen Gerris do), otherwise 

 it is difficult to understand how creatures of such fragile structure could survive 

 storms. They have been found only on the sea in warm latitudes, mostly in the 

 Atlantic, Indian, Pacific and Chinese regions, generally far from land, even as much 

 as 500 miles distant, but sometimes comparatively near the shore.* They are gre- 

 garious, but nothing certain is known of the nature of their food. On this point, 

 and also on the manner of their locomotion, especially as to the power of all the 

 species to dive, their enemies and means of defence, the use of several peculiar 

 structures, such as the ocelloid tubercles of the head, the ventral tubercle, and the 

 tarsal process, information is desired by the author. As he says, " A special interest 

 is attached to these animals, as being the only pelagic representatives of their class. 

 It is true that a few other insects are marine, but they are all found in close proximity 

 to the shore, whereas the species of Halohates usually, and in some cases only, occur 

 at a considerable distance from any land. Moreover, their structure would seem to 

 indicate that they are archaic forms of very great antiquity, and hence all that can 

 be learned with regard to them is of very great importance." 



Of the genus Halohates eleven species are described : 1, M. Wullerstorffi,\ 

 Frauenf. ; 2, H. micans, Esch. ; 3, H-princeps, 7i. sp. ; 4, H. Streatfieldanus, Tempi. ; 

 5, H. sobrinus, n. sp. ; 6, H. sericeus, Esch. ; 7, H. germanus, n. sp. ; 8, H. Hayanus, 

 n. sp. ; 9, H. proaDiis, n. sp. ; 10, H. flaviventris, Esch. ; 11, II. Frauenfeldanus, 

 E. B. White. 



Of the genus Ilalohatodes (n.g.) four species (one doubtfully congeneric) : 1, ZT. 

 Uluralns, Stul ; 2, H. kisirio, n. sp. ; 3, II. compar, n. sp. ; 4-, ? II. Stali, A. Dohrn. 



All the species, except the last mentioned, are figured by Mr. Edwin Wilson, 

 the excellence of the illustrations being vouched for by Dr. White. The number of 

 specimens extant in the museums of Europe or in private possession is not large, 

 but as far as possible they have been obtained and examined. The bibliographical 

 references are necessarily not numerous, but they have all been consulted, and the 

 most of them arc quoted verbatim. Altogether the subject has been well and ex- 

 haustively treated, as far as the available materials admit. 



* c. /., Mr. J. J. Walker's note, p. 93 antt. 



t All the specific names derived from proper names are printed without a capital initial letter 

 — niort insuLso ln'jas wlatis. 



