ARTHEOPODA — CRUSTACEA. 



101 



are not developed so constantly or to such an extent. Thus, Gall 

 the outline of the body is longer, more of the abdomen can 

 be seen from above, its last segment often bears small tail- 

 appendages, and in the female the first abdominal segment 

 also has traces of a pair of limbs, the gills are more numerous, 

 the cavities for the first feelers are not so clearly defined. 

 In these characters the Dromiacea approach the Macrura, 

 and it has been shown that they more particularly resemble 

 the true lobsters. A peculiarity, not derived from the 

 lobsters, is that in the DromJacea the last pair or two pairs 

 of thoracic legs are turned on to the back, where, by their 

 hooks or claws, they hold a bit of sponge or some such 

 object, under which the animal is completely hidden. It is 

 to this tribe that most of the early fossil Brachyura probably 

 belong, although this cannot be determined with certainty, 

 because the tender- skinned abdomen is very rarely preserved. 

 A starting-point for the tribe is furnished by Frosopon, 

 British specimens of which from the Great Oolite are here Table- 

 exhibited. First found in Bajocian beds, it persisted to 

 Neocomian times. The carapace, which alone is known, is 

 elongate and closely resembles that of Homalodromia, now 

 living in the West Indies, and apparently the most primitive 

 of recent Dromiidae. Another precursor of this family was 



Fig. 49.— An ancestor of the Crabs, Palxinachus longipes of the tribe 

 Dromiacea, Great Oolite, Wiltshire. (After H. Woodward.) 



Pcdaeinachns, found in the Forest Marble, fortunately with 

 its limbs ; unfortunately, however, the unique specimen is 

 not in the Museum, and its present whereabouts is unknown. 

 The restoration (Fig. 49) shows the primitive nature of the 

 carapace, abdomen, and limbs The English Gault has 

 yielded Homolopsis, which appears to lead from Frosopon 

 towards the family Homolidae. Dromiopsis, found in the 



