340 SYNOPTIC -COLLECTION. 



ment is large and has three pairs of leaf-like organs 

 attached to the ventral side. 



The many peculiar modifications of Serolis (No. 835) 

 are interesting. The body is flattened out and nearly 

 circular in outline as compared with most Crustacea. 

 The thoracic segments are narrow near the median line 

 and spread outward and downward surrounding the 

 shortened abdomen. Neither carapace nor rostrum is 

 present. The eyes are set in the head on the dorsal 

 side and the two pairs of antennae are flattened and 

 closely applied to the thoracic segments. These are the 

 only appendages visible 'from above. The mouth parts 

 and legs are all flattened and the latter are wide apart 

 on the edges of the body. 



Lygia dilatata St. (No. 836, dried specimen; No. 837, 

 alcoholic specimen), has a shortened depressed body cov- 

 ered like most of its kind by a chitinous exoskeleton. 

 This is divided into a small number of segments most of 

 which are distinctly seen, since Lygia has no carapace. 

 The head is small and fits into the first thoracic segment, 

 which is scooped out in front for this purpose. 



The seven thoracic segments are similar and constitute 

 the larger part of the body, while the six visible abdom- 

 inal segments are narrow and are crowded closely 

 together. 



The thoracic and abdominal segments are prolonged 

 laterally beyond the body proper, and the separate side 

 pieces thus formed are so freely movable that the body 

 can double upon itself. They also serve to protect the 

 appendages (excepting the first and last pair), so that 

 these are not seen in a dorsal view (No. 836) when the 

 crustacean is resting. 



The eyes are compound and are set in the head. One 

 pair of antennae are long and the other pair are very 

 short. The mouth parts are small and compact. The 

 seven pairs of jointed thoracic legs perform a similar 

 function and are similar in structure. 



