NO. 2063. NORTH AMERICAN PARASITIC COPEPODS— WILSON. 575 



The different genera show varying amounts of flexion and fusion and 

 we may separate the types as follows: 



1 . Tlie cephalothorax and trunk may be approximately in the same 

 straight line, when of course there is neither flexion nor fusion. 



These are large males, a millimeter or more in length; the mouth 

 tube, the antennae, and the first maxillae point forward in the same 

 direction as the body axis, or but little inchned to it and the anal 

 laminae similarly point backward ; the second maxillae and maxillipeds 

 extend outward at right angles to this axis. 



The trunk may be well segmented {Aclitheres and Thysanotella) , 

 partially segmented {Einhrachiella) , or wholly devoid of segmentation 

 (Thysanote, BracMella, and Vanhenedenia) . There is a carapace cov- 

 ering the entire body in Thysanote, a well-defmed cephalic carapace 

 in BracJiiella, a poorly defined one in Epibrachiella, and none at all in 

 the other three genera. 



2. The cephalothorax may be turned forward at right angles to 

 the trunk axis, so that the mouth tube, the antennae, and the first 

 maxillae point outward parallel with the second maxillae and maxilh- 

 peds; the anal laminae usually point outward also, though they may 

 point backward (Charopiiius) , or may even be turned dorsally 

 {Lernaeopoda) . The trunk may be well segmented (Charoinnus, im- 

 mature Lernaeopoda) , or may show no signs of segmentation (Pro- 

 IracJiiella, ParahracMella , adult Lernaeopoda). Lernaeopoda has a dis- 

 tinct cephaUc carapace, CJiaropinus has a larger but less distinct one, 

 while ParahracMella and ProhracMella have no trace of any. 



3. There may be two flexures, the mouth tube and antennae being 

 parallel with the greatly reduced trunk, as well as with the maxillae 

 and maxilMpeds, while the posterior portion of the cephalothorax 

 stands at right angles to all of them. This is found in the single 

 genus Lernaeopodina, whose males are considerably smaller than those 

 of the other genera already mentioned. 



We have here therefore complete flexion but no fusion; there is no 

 carapace visible and the trunk shows no traces of segmentation. 



4. There may be similar flexion combined with fusion so that we 

 can no longer distinguish the body regions. The sexual opening is 

 at the end of a rounded process just behind the second maxillae, and 

 extending outward parallel with them, and the anal laminae have 

 entirely disappeared. What was originally the long diameter of the 

 body may still be longer than the transverse diameter (Naohranchia, 

 Clavellopsis) or the latter may have increased sufficiently to exceed 

 the former {Clavellisa, Clavellodes) . The result in Clavellodes is 

 pecuhar; there is apparently an oblong body, squarely truncated at 

 one end, with the mouth tube and all the appendages arranged along 

 this truncation, paraUel with the long axis. But this is really the 

 same flexion that was seen in Lernaeopodina combined wdth complete 



