204 BRITISH TYROGLYPH1DJE. 



mandible found in both, there is a single exceptional 

 genus (Serrarius) with non-chelate saw-like mandibles, 

 forming an instance precisely similar to the present 

 genus. 



The Maxillary Lip, This is usually broad at the 

 base, but often drawn out to a narrow distal end, 

 membranous, very slightly chitinised, and forms a shelf 

 over which the liquid or semi-liquid food passes into 

 the mouth when driven by the palpal flagella. 



The Palpi (PI. Ill, figs. 1, 20; PL IV, fig. 7) form 

 another of the distinctive features of the genus ; they 

 consist of three joints, the proximal of which is said 

 by Megnin to be much longer than the others, and 

 wholly anchylosed to the maxillary lip ; the central and 

 distal joints being free. I am not quite able to agree 

 with Megnin ; in this I think there is a small third free, 

 or almost free, proximal joint. The distal joint is 

 usually the smallest, but is ordinarily slightly broadened 

 and flattened at its distal end ; it bears two flagella, 

 one at the actual distal end or antero -lateral angle, the 

 other on the outer side a very short distance back. 

 The anterior flagellum is always the longer when there 

 is a difference, and is generally directed forward and 

 outward; the posterior is often much shorter, and is 

 usually directed backward and slightly outward. In 

 some species, e. g. H. rostro-serratum, the two flagella 

 are of about equal length. The length of the anterior 

 flagellum, in proportion to the length of the whole 

 Acarus, varies greatly in different species. In addition 

 to the flagella the two distal joints of the palpus 

 usually bear a broad, thin, flexible, membranous border 

 to the whole or some part of their edge. The form 

 and arrangement of this membrane varies with the 

 species, but is not a regular even border in any species 

 where it has been described ; the two membranes some- 

 times run along the maxillary lip as well as the palpi, 

 and join together in the middle, forming a funnel down 

 which the liquid food passes into the mouth. 



The Notogaster in some species, such as H. rostro- 



