OR VST A GEASYSTEMA TIC BE VIE W 



297 



thorax. The 2 lateral eyes stalked (except In the 

 Cumacca). 



Order 1. Cumaoea. 



Shell (cephalo- thoracic shield) small, leaving 

 the 5 posterior free thoracic segments uncovered. 

 Eyes sessDe, close together or fused into one, 

 weakly developed, occasionally wanting. Two pairs 

 of foot-jaws. The first with a very large epipodite 

 carrying a gill. Of the 6 suhsequent pairs of 

 thoracic feet, the first 2 always can-y exopodites as 

 well as endopodites, the next 3 also often have 

 exopodites, but this is never the case with the last. 

 Abdomen long and slender. In the female the 

 pleopoda are wanting, excepting the last pair. 

 Marine form, Diastylis (Fig. 199). 



Order 2. Stomatopoda. 



Cephalo-thoracic shield rather small, not cover- 

 ing the 3 distinct posterior thoracic segments. Body 

 elongated, flattened dorso - ventrally. Abdomen 

 large and strong. The 5 anterior paii-s of thoracic 

 feet (oral feet because moved to near the mouth), 

 are holding or seizing feet with epipodial lamellse, 

 but mthout exopodites. The 3 posterior pairs of 

 thoracic feet are biramose limbs without epipodial 

 appendages. The 5 anterior pairs of pleopoda are 

 strong lamellated swimming feet, whose exopodites 

 carry branchial tufts. The 6th pair of pleopoda 

 forms with the telson a powerful caudal fin. The 

 heart with several paii-s of ostia is elongated into 

 a dorsal vessel running through the abdomen. 

 Ovaries and testes in the abdomen. Marine, Squilla 

 (Fig. 200). 



Order 3. Sohizopoda. 



Cephalo-thoracic shield well developed, like a 

 delicate integument covering the whole thorax. 

 The dorsal integument of the last 5 thoracic seg- 

 ments, or of the last thoracic segment, is not united 

 with it. The 8 pairs of thoracic feet are formed Sth thoracic segments ; a\-ab„Mo- 

 , ,., J -u- , -4.1 J., namal segments ; pi-pa, pleopoda ; 6r, 



pretty much alike, and are biramose (with exopodite g;iig_ 



and endopodite) ; we can, however, generally describe 



the 2 anterior pairs of thoracic feet as foot-jaws, as they may have masticatory 

 ridges. Abdomen strong, slender. Pleopoda very small in the female, strongly 

 developed in the male. The last pair of pleopoda, well developed in both sexes, 

 forms with the telson a rowing or swimming fin. Marine. 



Family 1. Mysidse. 



Thoracic feet without gills, the first pair with large vibratile epipodial lamellse. 

 Last 5 thoracic segments free under the dorsal shield. Auditory organs in the 

 endopodites of the 6th pair of pleopoda. Mysis, Siriella (Fig. 201) ; in the male, 

 gills on the pleopoda. 



Fig. 201.— Siriella Thompsonil, 

 male (after G. O. Sars). cth, Cephalo- 

 thoracio shield ; VII, VIII, 7th and 



