1 I 4 CRUSTACEA SYNCARIDA chap. 



The division Pekacaeida, including the Eucopiidae, Lopho- 

 gastridae, and Mysidae ( = Mysidaeea), the Cumacea, Isopoda, 

 and Ampliipoda, is characterised by the fact that when a carapace 

 is present it leaves at least four of the thoracic segments free 

 and uncoalesced : by the presence of a brood-pouch formed from 

 the oostegites on the thoracic limbs of the female : by the 

 elongated heart : by the few and simple hepatic caeca : by the 

 filiform spermatozoa : and by the direct method of development 

 without a complicated larval metamorphosis. The biting face of 

 the mandible has a movable joint, the " lacinia mobilis." ^ 



The division Eucakida, on the other hand, including the 

 Euphausiidae and the Decapoda, shows the converse of these 

 characters. The carapace coalesces with all the thoracic seg- 

 ments, there is never a brood-pouch formed from oostegites, the 

 hepatic caeca are much ramified, the heart is short, the spermato- 

 zoa are spherical with radiating pseudopodia, the development is 

 indirect with a complicated metamorphosis, and the mandible is 

 without a lacinia mobilis. 



Corresponding divisions are made by Caiman to receive the 

 other Malacostraca, namely, the Phyllocaeida for Nebalia, the 

 Syncarida for Anaspides, and the Hoplocaeida for the 

 Stomatopoda or Squillidae. 



The important array of characters which separates the 

 Euphausiidae from the other Schizopods and unites them with 

 the Decapoda can no longer be neglected, and the consideration of 

 Anaspides and its allies will further emphasise the extreme 

 difticulty of retaining the Schizopoda as a natural group. In 

 the sequel Caiman's proposed scheme will be adopted. 



DIVISION 1. SYNCAEIDA. 



There is no carapace, and all the eight thoracic segments may 

 be free and distinct. Eyes may be pedunculate or sessile. The 

 mandible is without a lacinia mobilis. There is no brood-pouch, 

 the eggs being deposited and hidden after fertilisation. The 

 spermatozoa arc filiform, the hepatic caeca very numerous, and 

 the heart tubular and elongated, with ostia only in one place in 



' The kcinia mobilis is a movable tooth-like structure joiuted on to the biting 

 faee of the mandible. 



