12 CALIFORNIA ACADEMY OF SCIENCES. 



consisting of a basal portion, the protopodite, and two 

 terminal rami. The first basal joint, the coxopodite, 

 or coxa, usually bears a branchial appendage, or epipo- 

 dite; the second joint, the basipodite, carries the two 

 rami; the inner ramus is called the endopodite, the 

 outer the exopodite. In the Decapods the endopodite 

 of the thoracic appendages is typically composed of five 

 joints which, counting from the basipodite, are desig- 

 nated as the ischium, merus, carpus, propodus, and 

 dactyl. In the appendages which precede and in those 

 which follow the thorax the endopodite is undivided, or 

 composed of less than five true joints. The appendages 

 will be described in their order from before backwards. 



The Eyes and Orbits. — The eyes in all of the Decapods 

 are compound and situated at the end of movable stalks. 

 These stalks, however, are probably not homologous 

 with the other appendages. The orbits in the Macroura 

 are generally represented by excavations in the anterior 

 margin of the carapace, but in the Brachyura they form 

 well defined cavities into which the eye-stalks can be 

 withdrawn. The number and position of the orbital 

 fissures are important characters for the purpose of 

 classification. 



The First and Second Antennce. — The first antennae, or 

 antennules, unlike the succeeding appendages, are not 

 typically biramous. It is true that they may bear two 

 terminal branches, or in some of the lower Macroura 

 even three, but it is quite clear that this condition is a 

 secondary one. The basal portion, or peduncle, nor- 

 mally consists of three joints, in the first of which is 

 located the auditory organ. In the Brachyura the 

 antennules are small, and located in cavities called 

 fossettes. 



