1 62 CRUSTACEA EUCARIDA DECAPODA chap. 



in all respects with the Nauplius of the Entomostraca. Secondly, 

 the thoracic limbs when they are first developed are biramous, 

 thus giving rise to the characteristic Mysis stage which links 

 the Macrura on to the " Schizopoda." Thirdly, the, order of differ- 

 entiation of the segments is typically from in front backwards, the 

 only precociously developed appendage being the sixth abdominal. 

 None of these characters are reproduced in the higher Decapoda 

 in which there is never a free-living Nauplius, the first larval 

 stage being the Zoaea ; a number of the thoracic pereiopods, and 

 usually all of them, are uniramous from the start ; and the whole 

 of the abdominal segments with their limbs tend to be precoci- 

 ously developed before the hinder thoracic segments make a dis- 

 tinct appearance. 



Tribe 3. Peneidea.^ 



The third legs are chelate except in genera in which the legs 

 are much reduced. The third maxillipedes are seven-jointed, the 

 second maxillipedes have normal end-joints, and the first maxilli- 

 pedes are without a lobe on the base of the exopodite. The 

 ])leura of the first abdominal segment are not overlapped by those 

 of the second. The abdomen is without a sharp bend. The 

 branchiae are usually not phyllobranchs. 



Fam. 1. Peneidae. — The last two pairs of legs are well 

 developed, and there is a nearly complete series of gills. Cera- 

 tasipisf a pelagic form. Parapeneus, Peneus, Aristaeus, etc. 



Fam. 2. Sergestidae. — The last or last two pairs of legs are 

 reduced or lost. The gill - series is incomplete or wanting. 

 Sergestes possesses gills, and the front end of the thorax is not 

 greatly elongated. Lucifer has no gills, and the front of the 

 thorax is greatly elongated, giving a very anomalous appearance to 

 the animal. All the members of this family are pelagic in habit. 



Fam. 3. Stenopodidae. — One or both legs of the third pair 

 al'e longer and much stouter than those of the first two pairs. On 

 a number of small anatomical points this family, including the 

 littoral genus Stenopus from the Mediterranean and other warmer 

 seas and Sjjongicola commensal with Hexactinellid sponges from 

 Japan, is separated by some authors in a Tribe by itself. 



^ Borradaile's useful paiieron the classification of the Decapoda (Ann. 3Iag. Nat. 

 ffist. (7), xix., 1907, p. 457) should be consulted for this and other Decapod 

 groups. Also Alcock's C'(i;<. of the Indian Mus., "Decapod Crustacea." 



- Giard and Bonnier, Covnit. Eciul. i>oc. Biol. 1892. 



