CONTRIBUTIONS TO MARINE BIONOMICS. 225 
in the middle, and the prelabial plate behind. It is flanked by the two 
basal joints of the second antenne in front, and by a forward process of 
the pterygostomial region of the carapace behind. Its floor is imperfect, 
and is formed by the anterior part of the third maxillipeds behind, and 
by a quadrangular sieve in front, furnished by the hairs springing from 
the two basal joints of the second antennz, the anterior pterygostomial 
processes, and a special anterior process of the fourth joint of the 
external maxillipeds. The hairs from all these parts are directed 
inwards towards the centre of the quadrangular space outlined by the 
boundaries of the prostomial chamber, and constitute a complete sieve- 
like floor to the chamber in question. On each side this prostomial 
chamber leads by a wide aperture into the branchial cavity. 
The participation of the epistome together with the prelabial space in 
the formation of a prostomial chamber is one of the features which 
strongly distinguishes the Corystoid crabs from typical Cyclometopa, 
Catometopa, and Oxyrhyncha. The arrangements of these parts approxi- 
mates in some respects to that found in the Oxystomata, where the 
buccal frame or the peristome is prolonged anteriorly as a definite 
prostomial chamber to the very tip of the snout. This chamber in the 
Oxystomata, however, is completely closed in by the third maxillipeds, 
and is very narrow anteriorly ; in the Corystoidea, on the other hand, it 
is broad in front, and is imperfectly closed by the third maxillipeds. 
III, PREVIouS OBSERVATIONS ON HABITS. 
In Bell’s “ British Stalk-Eyed Crustacea” (1853) a brief reference is 
made to the sand-burrowing habits of Corystes cassivelaunus. Couch 
had already described the crab as “burrowing in the sand, leaving 
the extremities of its antenne alone projecting above the surface.” 
The actual process of burrowing appears not to have been observed 
at the time when Bell wrote, for he quotes Couch’s suggestion that the 
elongated antennz possibly “assist in the process of excavation.” This 
theory of the function of the antennze was subsequently rejected by 
Gosse (1865), as a result of his own observations on the habits of the 
crab, and again by Hunt (1885), who correctly states that the crab 
descends into the sand backwards with the greatest agility, “thus leaving 
the antennz no opportunity of assisting in the operation.” 
The first writers to offer anything approaching a real explanation of 
the use of the antennsz were the veteran naturalist of Cumbrae, 
Mr. David Robertson, and Mr. P. H. Gosse. It is difficult to say, and 
would indeed be ungenerous to enquire, which of these two naturalists 
has the priority in the matter. Gosse, in 1855, described the outer 
antenne of Corystes as “together forming a tube” (Manual of Marine 
