766 CRUSTACEA. 



Genus JEGcA., Leach. 



Mga EFFERATA. 



Corpus sat angustum, nudum. Segmenta thoracis subosqua, segmentis 

 quatuor posticis quoad epimeras acutis et strict^ appressis. Abdomen 

 ft-artiadatum, thorace subito angustius, lateribus parallelis, articulo 

 sexto subtriangulato, ad basin latiore, laiitudine parce breviore, extre- 

 mitate rotundato et eiliato. Appendices caudales abdominem vix supe- 

 rantes, apice rotundatce, angxdo basis interna producto et acuto, lamelld 

 internd paulo longiore, duplo latiore. 



Body rather narrow, naked. Segments of thorax subequal, four pos- 

 terior segments having the epimerals acute and closely appressed. 

 Abdomen six-jointed, abruptly much narrower than thorax, sides 

 parallel, sixth segment subtriangular, broadest at base, slightly 

 shorter than its breadth at base, extremity rounded and ciliate. 

 Caudal appendages scarcely extending beyond abdomen, rounded at 

 apex, inner angle of base prolonged and acute, inner lamella a little 

 the longer and twice the broader. 



Plate 51, fig. 1 a, animal, enlarged; b, antennae; c, one of the 

 three anterior pairs of legs; d, one of the four posterior pairs; e. 

 caudal stylet. 



From a Serranus (?), harbour of Rio Janeiro. December, 1838. 



Length, three lines. Colour, yellowish. Head short, posterior 

 margin concave, and applied against the entire convex anterior mar- 

 gin of first thoracic segment. The acute angle of the four posterior 

 thoracic segments belongs properly to the epimerals. Four anterior 

 abdominal segments equal and similar; sixth about as long as five 

 preceding. Caudal lamellae extend to same line with apex of abdo- 

 men ; the ciliation rather long, being nearly two-thirds as long as the 

 branches. Anterior margin of first pair of antennae on a line with 

 the front margin of the head ; basal joints followed by five shorter 

 and smaller ; second pair one-half the longer, not one-third the length 



