54 PROFESSOR GEORGE H. CARPENTER 



DESCRIPTION OF SPECIES. 

 Isotoma Brucei, sp. nov. Plate, figs. 1-8. 



Length 175 mm. Feelers as long as head. Six ocelli on each side of head (fig. 2). 

 Ridge surrounding the post-antennal organ elongate and narrow (fig. 2, p. a. o.). Feet 

 without tenent hairs, claws slender and untoothed (fig. 5). Spring evidently borne on 

 the fourth abdominal segment, slender and elongate, one-fourth length of insect ; 

 manubrium longer than dens ; mucro short, with a prominent thick terminal tooth and 

 two strong basal teeth (figs. 1, 6, 7). Colour slaty grey, the pigment somewhat 

 scattered. Hairs on body short, a very few strong bristles on the tail segment. 



Locality. Laurie Island, South Orkneys. Innumerable specimens on the sea- 

 shore on the carcase of a penguin. 9th January 1904. 



The discovery of this insect in the Antarctic regions is of very great interest on 

 account of its close relationship to the Arctic and sub- Arctic /. Beselsii, Packard.* In 

 the general build of the body and the structure of the spring particularly the form of 

 the mucro, with its three prominent claw-like teeth these two species of Isotoma 

 stand apart from all other members of the genus. /. Brucei is somewhat smaller than 

 /. Beselsii, and has the spring, especially the dens, relatively longer and more slender ; 

 the mucro relatively longer and narrower and its teeth weaker. These differences are, 

 however, less apparent in young individuals. In the shape of the ridge surrounding 

 its post-antennal organ, /. Brucei agrees closely with I. Beselsii ; but while the latter 

 has the sixteen ocelli which are usually present in species of Isotoma, the former has 

 only twelve, the two posterior ocelli of the inner row of four, on each side, being absent. 

 The antennal organ consists, as in /. Beselsii, of two prominent hemispherical papillae 

 at the extreme apex of the fourth antennal segment (fig. 2, a. o.). The feet in the 

 present species have, as in /. Beselsii, untoothed claws and no tenent hairs ; the apex 

 of the smaller claw is, however, drawn out in a slender process, which is not so fully 

 developed in the northern species. 



The mouth-parts of Isotoma Brucei show several interesting peculiarities. The 

 mandibles are remarkably narrow and parallel-sided at the apex (fig. 3), and exhibit 

 two very prominent acuminate processes at the hind dorsal corner of the grinding area 

 (fig. 3, mo.}. The maxillulse (fig. 4, mxl.) have prominent apexes, armed with several 

 stout curved bristles ; the spines, arranged in series along the inner edge of the basal 

 region of the maxillula, are elongate and sharp-pointed. 



In the structure of the maxilla (fig. 4, mx.) I. Brucei differs from other 

 species of Isotoma, and indeed from members of its family generally, by the 

 slender and elongate form of the " head" (compare the typical semi-globose " head " of 

 Cryptopygus, fig. 19). The head in the present species is composed of a strongly 



* Isotoma spitzbergensis, Lubbock. See CARPENTER and EVANS (1899), SCHAFFER (1900). The species is recorded 

 by WAHLGREN (1906) from Tierra del Fuego. 



(ROY. soc. or EDIN. PROC., VOL. xxvi., PP. 474-475.) 



