KEY TO ALL KNOWN SPECIES OF SEROLIS 281 



b. Terminal segment with a conspicuous median dorsal keel; posterior extremity 

 narrow and rounded ; dorsal surface of body without median or lateral tubercles 



25. 5. bakeri, Chilton. 



c. Terminal segment with slight median dorsal keel ; tubercles on cephalosome and 



on thoracic somites absent ... ... ... ... ... 26. .S. j'OKj'e!, Hale. 



IL Coxal plates of seventh thoracic somite extending backwards beyond the posterior 

 extremities of the pleural plates of the second and third abdominal segments. 



a. Pleural plates short, not extending beyond the broad anterior margin of the 

 terminal segment; terminal segment triangular in shape with rounded angles, 

 slight median dorsal carina present ... ... ... ... 27. S. orbiculata, n.sp. 



b. Pleural plates of second and third abdominal segments extending beyond the 

 anterior margin of the terminal segment; those of the third slightly the longer. 



1. Terminal segment with median dorsal and two lateral carinae on either side, the 

 outer one of which follows the outline of the terminal segment 28. S. noiotropis, n.sp. 



2. Terminal segment roughly five-sided, with a well-developed spine in an antero- 

 median position on the dorsal surface, followed by a low median carina, on 

 either side of which are two lateral carinae each terminating in a small spine 

 some distance from the lateral margin ... ... 29. S. pagenstechen',I'ief[er. 



. Hindmost suture of sixth thoracic somite obsolete in the mid-dorsal line, so that for a 

 short distance the terga of the sixth and seventh somites are fused with each other and with 

 that of the first abdominal segment. 



L Position of missing suture between the sixth and seventh somites indicated by a groove ; 



uropod very small, endopod wanting ... ... 30. S. platygaster, n.sp, 



II. Groove absent. 



a. Coxal plates of seventh thoracic somite of male produced backwards for a short 

 distance beyond the attachment of the uropod, and beyond the level of the pleural 

 plates of the third abdominal segment; those of female extending backwards as far 

 as the pleural plates of the third abdominalsegment, which, in both sexes, are longer 

 than those of the second. 



1. Margins of coxal and pleural plates and of terminal segment very much 

 thickened 3^- S. bouvieri, Richardson. 



2. Margins not thickened; terminal segment with a well-developed spine in 

 antero-median position, followed by a median carina, on either side of which 

 are two lateral carinae terminating at some distance from margins in small 

 spines 32. S. aspera, n.sp. 



b. Coxal plates of seventh thoracic somite not reaching backwards as far as the attach- 

 ment of the uropod. Pleural plates short. 



1. Coxal plates of seventh thoracic somite of male extending backwards to Just 

 beyond the pleural plates of the third abdominal segment; surface of body 

 covered with tubercles 33. 5. fl;«?;a//e«s/.f, Beddard. 



2. Coxal plates of seventh thoracic somite extending backward to the level of the 

 extremities of the pleural plates of the second abdominal segment but not as far 

 as those of the third. 



a. Each of the segments of the body with a dorsal median curved, hook-like 

 spine, and with a row of short tubercles near its hinder border 



34. S. elongata, Beddard. 

 j8. Segments with median spines and lateral tubercles. Terminal segment long, 

 with incurved sides, and with posterior truncate extremity concave 



35. S. longicaudata, Beddard. 



