MODIFICATIONS OF STRUCTURE IN DECAPOD CRUSTACEA. 221 



Lupa or Callinectes. All the species of this genus are 

 remarkably specialised for burrowing in sand, as indicated by 

 the great compression of the four hindmost thoracic pairs of 

 legs, and by the spade-like modification of their terminal 

 joints (cf. Rumphius, 1705, and Krauss, 1843). 



The chelipeds are curved and moulded to fit the sides of the 

 carapace during flexion, exactly as in the genus Atelecy- 

 clus. They are destitute of the cockscomb-like crests 

 which furnish such a characteristic feature of the genus 

 Calappa. The anterior part of the buccal apparatus is con- 

 sequently exposed even during flexion of the chelipeds. The 

 protection of the mouth parts is, however, ensured by the 

 forward prolongation of the external maxillipeds (fig. 2, b), a 

 feature which is not to be observed in the genus Calappa, 

 but which is a marked characteristic of the allied Leucosiidge. 



If I am right in my interpretations, the exostegal canal in 

 this crab has a most extraordinary course. The orbits, in 

 which the eye-stalks are retractile, have the form of a pair of 

 stony cups. The outer and inferior angle of the orbit is, 

 however, incomplete, and its cavity is continued downwards 

 and outwards over the pterygostomial regions by a deep semi- 

 cylindrical gutter (fig. 2, e). This gutter is converted into a 

 tube by two dense rows of hairs which arise from the inner 

 and outer edges of the gutter, and by their interdigitation 

 beneath the cavity of the gutter furnish it with a complete 

 hairy floor. So closely are the hairs set to one another, and 

 so intimately do they interlock, that upon a cursory examina- 

 tion the hairy nature of the floor of the orbital gutter is not 

 at first suspected, and Hilgendorf actually figures the gutter 

 (1869, fig. 2) as a completely tubular passage excavated in 

 the substance of the thick calcareous wall of the carapace. 



The orbital gutter, as soon as it loses its tubular appear- 

 ance, turns obliquely outwards and backwards (fig. 2,/) until 

 it is lost in a thick carpet of hairs, which is especially well de- 

 veloped in front of and to the outer side of the aff'erent aperture 

 at the base of the chelipeds, but which is also continued back- 

 wards along the whole inferior edge of the branchiostegite. 



