104 ILLUSTRATIONS OF SOME SPECIES OF 
female of Rhagigaster differing from those of all the four other 
species now represented by possessing ordinary-shaped 6-jointed 
maxillary palpi, like Diamma and Methoca; from the first of 
which it is at once distinguished by its depressed (not compressed) 
form, and by its nearly simple (not multidentate) mandibles. Not- 
withstanding these very evident distinctions, M. Guérin has 
described a female of Rhagigaster as a second species of Diamma, 
as above noticed, and has further increased the confusion by 
asserting that D. bicolor is the female of Rhagigaster ; whereas, 
there is great reason for considering that it is the female of 
Tachypterus (Psamatha, Shk.), which has the mandibles more 
toothed than in the majority of the family, although the female 
possesses one more tooth than the male, which is not the case in 
the other species, of which the sexes have been determined : indeed 
the contrary occurs in the majority. 
The discovery of the female of Myzine will moreover determine 
whether the small rudimental vein inclosed within the first sub- 
marginal cell of Rhagigaster (which is the only character by which 
it is distinguished from Myzine ¢), does not indicate a much more 
marked difference in the opposite sex than might at first be 
supposed to be the case, or whether it is sufficient to bind it, as it 
now does, to the other Thynnideous insects. 
The following are the characters of the genus Rhagigaster, as 
modified and extended by the examination of ‘several species, and 
by the discovery of the female sex, together also with a synopsis 
of the species which belong to it. 
RHAGIGASTER, GUERIN. 
¢ Abdomen elongatum apice spina recurva armatum, segmento primo subtus tuberculo conico 
instructo ; segmentis 2ndo et reliquis ad * basin constrictione subarticuliformi instructis. 
Frons inter partem superiorem oculorum subcarinatus. 
Mandibule intus versus apicem dente armate. 
Ale antic cellulis 4submarginalibus, prima appendiculata. 
Palpi omnes forme ordinariz. 
Clypeus antice fere recte truncatus. 
Labrum margine antico vix emarginato clypeo fere abscondito. 
9 Caput magnum subquadratum planum impressione longitudinali utrinque pone occulos. 
Mandibule et palpi mari conformes. Thorax 3-annulatus, apterus, 
Abdomen elongatum depressum segmentis ad basin linea tenui transversa impressis. 
* M. Guérin erroneously describes the abdominal segments as having ‘en arriére, ainsi 
que le premier une impression transverse.’ The lateral examination of the abdomen at once 
shows that the first segment is not constricted, and that it is the base and not the extremity 
of the other segments which is thus circumstanced. 
