a Gemis of Dipterous Insects. 285 



cies of Chnicidcc 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 ]8, and described as the Cimex lineola of Linnaeus, has been recently 

 raised to the rank of a genus by Ilahn under the name of Largus, and by 

 Laporte under the name of Euri/ophthalmus. It is the Cimex humil'is of Drury, 

 punctatus, De G., and puncticoUts, 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 ayeux de Crabe" (fig. 17-), the peduncles are at least as 

 long as the breadth of the head. The Astemma cornuta of St. Fai'geau and 

 Serville {Encycl. MM. 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 antennae 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 otlier 

 classes and orders ; and as these instances involve in some degree the doctrine 

 that eveiy aflSnity 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 Criistacea 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 Squ'iUa 

 (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 Achceus 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 LatreiUia of Roux (jCrustacds de la Mediterr., pi. 22.) ; but 

 the peduncles of the eyes are very long. The preceding are instances from the 

 family of Spider Crabs, Muiidce, Westw., or Crabes triangulaires of Latreille. 



* Leach, Malacost. Podophtk., tab. 22. 

 2 p2 



