512 



CRUSTACEA. 



Lastly, we may notice that a Phyllopod nearly allied to the living 

 fresh-water genus Branchipus .has been detected by Dr Henry Wood- 

 ward in the Eocene formation, and has been described by him under 

 the name Branchipodites vectensis. The much older Branchipusites 

 (rightly Branchipodites) anthracinus, of the Coal-measures, has been 

 supposed to have similar relationships, but it does not appear to be 

 truly a Phyllopod. 



Order III. Phyllocarida. — This order was founded by Packard 

 to include the recent genus Nebalia along with certain extinct types 

 of the Crustacea, which in some respects form a connecting-link 

 between the Phyllopods and the Malacostracous group of the Schiz- 

 opods, though they appear to be properly referable to the Branchi- 

 opoda. The principal living form of the Phyllocarida is Nebalia, 

 which must be regarded as constituting 

 with its immediate allies the family of the 

 Nebaliadcs, and which must be taken as 

 giving the essential characters of the order. 

 In the genus Nebalia (fig. 364), the an- 

 terior part of the body is covered with a 

 folded, but unhinged, cephalothoracic shield 

 or carapace, which is connected with the 

 body in its cephalic part only, and extends 

 down the sides so as to enclose the mouth 

 organs and the greater part of the other 

 appendages. The valves of the carapace 

 are not separated along the back, but are 

 moved by an adductor muscle. In front 

 of the carapace, and movably articulated 

 to it, is a rostral plate ; and there are also 

 two compound stalked eyes, the cornea 

 of which is not faceted. Two pairs of 

 antennae are present. The segments of 

 the thorax, though enclosed by the cara- 

 pace, are free, and carry eight pairs of 

 foliaceous feet, which are of the " phyllo- 

 podous " type, and officiate as branchiae. 

 The abdomen is composed of free rings, 

 the first four somites of this region carry- 

 ing as many pairs of biramose legs, while 

 there are also two pairs of rudimentary caudal limbs. No telson 

 is present in Nebalia and its allies, but there is a well-developed 

 telson in the Ceratiocaridce. There is no metamorphosis in de- 

 velopment. 



The living types of the Phyllocarida belong to the genus Nebalia 

 and the closely related Nebaliopsis and Para nebalia, and are all small 



Fig. 364. — Nebalia Herbstii, en- 

 larged about three times. Recent. 



