THE LARViE OF CERTAIN BRITISH CRAXGONIDiE. 



597 



long, downwardly-curved blunt process, which in later stages has 

 the form of a long hooked spine. The tail plate is of the usual 

 form. The first antennae are very long — about two-thirds of the 

 length of the carapace. The inner flagellum is bluntly pointed and 

 ciliated in the first stage. The scale of the second antenna is long 

 and very narrow, with only six internal setoe, two setse and a spine 

 terminally, and two short external setae. The palp of the first 

 maxilla is two-jointed. The remaining appendages I will here leave 

 undescribed. 



The larva of ^gcon fasciatus can be at once distinguished 

 by the length of the antennae and the spines of the abdominal 

 segments, the two lateral spines of the fifth segment with their 

 terminal hook being very conspicuous, especially in the later stages. 



TABLE FOR THE DISCRIMINATION OF SPECIES 

 HITHERTO DESCRIBED. 



1. 



* Palp of first maxilla one-jointed . 

 Palp of first maxilla two-jointed . 



2. Third abdominal segment with a dorsal spine 

 Third abdominal segment without a dorsal spine 



3. Abdomen more than twice as long as thorax 

 Abdomen less than twice as long as thorax 



4. Telson deeply incised; posterior dorsal margin 



of abdominal segments smooth 

 Telson not deeply incised ; posterior dorsal 

 margin of abdominal segments with many 

 small spines . . . . 



5. Telson with more than sixteen spines 

 Telson with fourteen to sixteen spines 



6. No dorsal spines on abdominal segments . 



7. Spines of fifth abdominal segment long, curved 



downwards at the end 

 Spines of fifth abdominal segment short and 

 pointed, or absent . . . . 



8. Third abdominal segment with no dorsal spine 

 Third abdominal segment with two dorsal spines 



9.f Inner flagellum of first antenna with cilia only 

 Inner flagellum of the first antenna with cilia 

 and small spines . ... 



2. 

 3. 



Cranrjon vulgaris. 

 0. allmatmi. 

 4. 

 5. 



PontopMltis spinosus. 



P. norvegicus. 



6. 



7. 



Sahinea septemcan'nafa. 



jiEgeon fasci'dus. 



8. 



C. trispinosus. 



9. 



C. echimdatus. 



C. nanus. 



* The mysis stage of Crangon differs from that of the other genera in having exopodites 

 on the first four thoracic appendages only, instead of on the first five pairs. 



t In the first larva only. In later stages the larvae must be distinguished by size, 

 e.g. last stage : C. ecfmiulatus, 4'80 mm. ; C. iianus, 3'30 (Sars). 



