a Genus of Dipterous Insects. . 285 
cies of Cimicide with ocular peduncles, in the 34th plate of his 3rd volume, 
fig. 17, 24, and 25, all from Surinam; of these, that represented in fig. 17 
and 18, and described as the Cimex lineola of Linnzeus, has been recently 
raised to the rank of a genus by Hahn under the name of Largus, and by 
Laporte under the name of Euryophthalmus. It is the Cimex humilis of Drury, 
punctatus, De G., and puncticollis, Laporte: the footstalks are very short, at 
least such is the case in a specimen which I have received from Brazil; but 
in De Geer's “ Punaise à yeux de Crabe” (fig. 17.), the peduncles are at least as 
long as the breadth of the head. The Astemma cornuta of St. Fargeau and 
Serville (Encycl. Méth. x. 323.) has also the eyes placed upon peduncles nearly 
a line long. It is from Cayenne, and appears nearly allied to the latter. In 
none of the preceding instances, however, do the footstalks acquire the remark- 
able length which they possess in Diopsis, nor are the antenne situated upon 
them. 
But this lateral prolongation of the head into ocular peduncles is not con- 
fined to insects, strictly so called, but is found in a few instances in other 
classes and orders; and as these instances involve in some degree the doctrine 
that every affinity is connected with, and must be tested by, a corresponding 
analogy, I shall detail them, without, however, offering any opinion upon the 
doctrine itself. : 
In the class Crustacea we find that Dr. Leach applied the term Podoph- 
thalma to the great typical group containing the Crabs (order Brachyura), 
and Lobsters and Shrimps (order Macrura), as well as the genus Squilla 
(order Stomapoda), which last he did not consider as entitled to the rank of 
an order. In all these animals the eyes are carried upon footstalks moveable 
at the base, so that the eyes are retractile within the anterior cavities of the 
_ shell. In some instances, however, they are fixed, as in the Dipterous insects 
mentioned above. This occurs in the genus Æchæus of Leach, according to 
whom* “it is the only known genus of Brachyura, except Leptopodia, whose 
eyes are not retractile.” To these two genera is very nearly allied the recently 
established genus Latreillia of Roux (Crustacés de la Mediterr., pl. 22.) ; but 
the peduncles of the eyes are very long. The preceding are instances from the 
family of Spider Crabs, Maiide, Westw., or Crabes triangulaires of Latreille. 
* Leach, Malacost. Podophth., tab. 22. 
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