CALIFORNIA STALK-EYED CRUSTACEA. 15 



The Gills. — The gills may be situated on the basal 

 joints of the thoracic appendages (podobranchise), or 

 on the articular membranes between the legs and the 

 body (arthrobranchiaB), or on the sides of the thoracic 

 segments (pleurobranchise). There are two types of 

 gills — the trichobranchiee, in which there are thread- 

 like, branchial filaments arranged around a common 

 stem, and the phyllobranchias, in which the stem bears 

 on each side a row of thin, transverse lamellae. 



A few other structures deserve mention in this con- 

 nection, viz.: — the epistoma, the area lying in front of 

 the buccal, or mouth area and behind the antennules; 

 the upper lip, a fleshy projection in front of the mandi- 

 bles; the loivei^ lip, a flap lying behind the mandibles; 

 the thoracic sternum, or sternal plastron, the ventral por- 

 tion of the thorax, and the terminal segment of the 

 Macrouran abdomen, the telson. 



Tribe BRACHYURA. 



Carapace broad. Orbits well defined. Antennules lodged in fossettes. 

 Antennae short and devoid of an acicle. The external maxillipeds have 

 the ischium and merus flattened and usually fitted neatly to the buccal 

 area. First pair of legs always chelate; the following pairs always simple. 

 The abdomen is small, shorter than the carapace, and flexed against the 

 ventral surface of the thorax. The abdomen of the male is smaller than 

 that of the female and bears but one or two pairs of appendages near the base; 

 abdominal appendages in the female more numerous than in the male and 

 used for holding the ova. Tail fin absent. 



The subdivisions of the Brachyura can usually be 

 recognized by their general form. The Maioidea, or 

 spider crabs, have the carapace narrowed in front 

 where it is generally produced into a rostrum. The 

 Cancroidea usually have a transverse carapace with a 



