KEY TO PHYLA 21 



37. (40) Two or three conspicuous caudal setae. (Some 

 larvae with two projections from the posterior extremity of the 

 abdomen have no gills on either thorax or abdomen. These are 

 Coleoptera (larvae). If gills are present along sides of either 

 thorax or abdomen go on with 38) 38 



38. (39) Three caudal setae; gills on sides or abdomen; tar- 

 sal claws single (see fig. 14) ORDER EPHEMERIDA (nymphs) 



39. (38) Caudal setae usually two; gills mainly under tho- 

 rax. Tarsal claws two (see fig. n) 



ORDER PLECOPTERA ( nymphs ) 



40. (37) With no caudal setae 41 



41. (42) Abdominal segments provided with long lateral fil- 

 aments or tufts of hair-like projections along either side, or in 

 some cases the last two abdominal segments only are supplied with 

 lateral rows of hair-like projections (see fig. 9) 



ORDER COLEOPTERA ( larvae ) 



42. (41) Abdomen ending in a median non-segmented tail- 

 like process ORDER NEUROPTERA (larvae, in part) 



43. (36) Mouth parts in the form of a jointed beak directed 

 backward between the bases of the forelegs, often closely applied 

 to body ORDER HEMIPTERA (nymphs) 



44. ( i ) Head provided with two pairs of antennae in addi- 

 tion to any feeler-like organs which occur in the region immedi- 

 ately around the mouth opening. Never with wings. Respiration 

 by means of gills, or in some small forms directly through the 

 skin. Mostly aquatic. CLASS CRUSTACEA 45 



45- (5) With a bivalve shell hinged along dorsal surface, 

 covering at least part of body and enclosing not only body wall 

 but also the appendages 46 



46. (49) Entire body, including appendages and head, en- 

 closed in a shell ; resembling a small mussel 47 



47 (48) With but two pairs of trunk appendages 



SUBCLASS OSTRACODA 



