1 84 



CRUSTACEA — EUCARIDA— DECAPODA 



stock, and hence that the development of the Brachyura ran 

 through an Anomurous strain ; but Huxley, and latterly Bouvier/ 

 adopt the view that the Dromiacea are descended^ not from the 

 Galatheidae, but direct from the Macrura, and especially from 

 the Nephropsidea. Special resemblances are found between the 

 Jurassic Nephropsidae and certain present day Dromiacea, e.g. 

 Homolodromia 'paradoxa, the detailed form of the carapace in the 

 two cases being very similar. It is, however, a little strange 

 that in the Dromiacea we meet with the same reduction and 

 dorsal position of the last, or last two pairs of thoracic limbs 

 which we saw to be such a characteristic feature of the Anomura, 

 especially of the Galatheidae. In the Dromiacea these limbs may 

 be chelate, and they are used for attaching shells and other 

 bodies temporarily to the back. Must we suppose that this 

 resemblance to the Anomura is due to convergence, or that the 

 Nephropsidae, which gave rise to perhaps both Galatheidae and 

 Dromiacea, had this character, and that it has been subsequently 

 lost in the Macruran stock ? We have already mentioned that 

 the Metazoaea of Dromia has not only a well-developed swim- 

 ming third maxillipede, but also a Inramous first pereiopod, a 

 character which speaks strongly for Macruran affinities. 



Fam. 1. Dromiidae. — The eyes and antennules are retractile 



into orbits. The last two 

 pairs of thoracic limbs are 

 small, and held dorsally. 

 The sixth pair of pleopods 

 are rudimentary or absent. 

 Homolodromia from West 

 Indies, deep - sea. Dromia, 

 widely dispersed. D. vtdgaris 

 (Fig. 126) occurs on the 

 English coasts. 



Fam. 2. Dynomenidae. — Similar to the preceding family, 

 but only the last pair of tlioracic limbs is small, and held dorsally. 

 The sixth pair of pleopods are reduced, but always present. 

 Ihjnomene in the Indo-Pacific. 



Fam. 3. Homolidae. — The eyes and antennules are not 

 retractile into orbits. Only the last pair of thoracic limbs are 

 reduced, the sixth pair of pleopods altogether absent. Homola 



^ Loc. cit. p. 183. 



Fig. 126. — Dromia rnlgaris, x 1. (After 

 Milne Edwards and Bouvier.) 



