ART. 10 LARVAE OF GKAPSID CRABS HYMAN. 3 



method of distinguishing closely related forms is not now available. 

 The eyes of Planes are relatively very large and its pigmentation 

 unusually heavy. The eyes of Pachygrapsus are much smaller. 



FIRST ZOEA (fig. 21). 



Gephalothorax. — The dorsal and rostral spines are short and stout. 

 Both pass outward perpendicularly to the long axis of the body. 

 Cephalic appendages: The antennule (fig. 27) is a single segment 

 and carries sensory hairs and a seta. The antenna (fig. 27) is in 

 the form of a strong spike that carries an extremely minute exopodite. 

 The spike is hairy near its tip. The other cephalic appendages (figs. 

 33 and 37) have the usual brachyuran form. 



Thoracic appendages. — These have the usual brachyuran form. 

 The first and second maxillipeds carry four swimming hairs. 



Abdomen. — The telson (fig. 55) is bicornuate and its horns pass 

 backward almost parallel with each other. There are three spines 

 on the median surface of each cornu. The lateral surface is smooth 

 and does not show a spine. 



SECOND ZOEA, 



The second zoea is not known. The form described by Cano as 

 the second zoea is doubtless the third stage. 



THIRD ZOEA (fig. 22). 



The second zoeal stage represented by Cano is probably the third 

 zoeal stage. Cano shows only four swimming hairs on the maxil- 

 lipeds, but this probably was due to error. They probably had as 

 many as seven or eight hairs. The fact that the scaphognathite is 

 well developed (fig. 38) indicates that the stage is advanced beyond 

 the second zoeal. A more careful examination of this stage probably 

 would show the anlagen of the endopodites of the antennae and of the 

 abdominal appendages. 



FOURTH ZOEA. 



The fourth zoeal stage seems to have been overlooked by Cano. 



FIFTH ZOHJA (fig. 23). 



The third stage described by Cano shows the condition character- 

 istic of the last zoeal stage. This is the fifth stage in the Xanthidae 

 and Ocypodidae. There are eleven or twelve swimming hairs, the 

 mandible shows a palp, and the thoracic appendages are fully articu- 

 lated. 



Cephalic appendages. — The antennule (fig. 28) shows a base of 

 three segments and, distally, an endopodite of four segments each 

 bearing two or three sensory hairs and an unsegmented smooth 

 exopodite. The coxal segment is enlarged for the statocyst. 



