622 Mr. J. O. Wzsrwoop on the Pausside, 
mis (priori pauló majori, globoso); ultimo magno, longè 
ovato, aut cylindrico-subnlato, apice acuto. Thorax sub- 
cylindricus, pauló longior quàm latior, antice plerumque 
dilatatus, parte elevaté anticá plùs minüsve articuliformi. 
Elytra posticé truncata. 
The characters given above will at once separate the species 
of the genus from their immediate affinities, the palpi mate- 
rially assisting in tracing the boundaries of the genus. 
It will be observed that Afzelius (who, notwithstanding his 
admitted inability satisfactorily to examine the trophi of the 
genus, has given their characters drawn from an external com- 
parison of P. microcephalus and spherocerus,) has, as might have 
been expected, fallen into several errors, chiefly regarding the 
nomenclature of the different parts :—thus his palpi interiores are 
the labial palpi; his palpi exteriores, the anterior produced lateral 
lobes of the mentum; his mandibule, the maxillary palpi; his* maz- 
ille are the mandibles ; and his gula triangularis is the mentum. 
This author, however, most properly considered the flat plate- 
like part which closes the underside of the mouth, as the lower 
lip (labium); and (with the exception of the anterior lateral lobes 
of the mentum being incorrectly articulated, to represent palpi, 
as they were considered ; and the maxillary palpi being repre- 
sented as without joints, being regarded as the mandibles,) his 
figures of the underside of the heads of both species correctly 
exhibit the general structure of the various parts of the mouth 
as seen externally. 
Latreille, however, both in the Histoire Naturelle and Genera 
Crustaceorum, $c. appears to have regarded the organs, which 
Afzelius described as the external palpi, and which I have de- 
* [t must be borne in mind that Afzelius is not blameable for this variation of 
nomenclature, since it was in accordance with that of Fabricius, adopted by him.— 
See Kirby and Spence, vol. iii. p. 429. 
scribed 
"n Mu Lu c E eae 
