l8 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



The telson has been regarded by some as representing the 

 last segment of the abdomen, but Delia Valle and others regard 

 it as simply a development of the posterior end of the rectum, in 

 the nature of an anal valve, morphologically equivalent to the 

 upper lip which will be described below. The telson may have 

 the form of simply a thin oval projection as in Lysianopsis and 

 Calliopius. In Amphithoe, Grubia, Sympleustes, and Unciola 

 it is also a simple plate but somewhat thicker than in the pre- 

 ceding genera. In Microdeutopus the rectum passes directly 

 through the telson, which is undivided. The telson may be more 

 or less deeply divided into two lobes as seen best in the Gam- 

 maridae where the lobes are usually rather widely separated from 

 each other and armed apically with a fascicle of spines. 



/ 



APPENDAGES. 



Each segment of the crustacean body normally bears a single 

 pair of appendages upon the ventral side so that in those forms 

 in which two or more segments are fused together the number of 

 appendages affords a criterion of the fundamental segmentation. 

 In the head region of the Amphipoda, however, the difficulty of 

 determining the number of true segments lies in the fact that 

 an uncertainty exists regarding the homologies of some of the 

 appendages. According to most students of the group, the 

 head is made up of seven segments which bear the following 

 appendages from in front backwards : eyes, first or superior 

 antennae, second or inferior antennae, mandibles, first and second 

 maxillae, and maxillipeds. The last are regarded as homologues 

 of the first maxillipeds of the Decapoda, and as such are 

 fundamentally appendages of the thorax and not of the head. 



The mouth parts form the buccal mass projecting from the 

 ventral side of the anterior end of the head. The buccal mass 

 is especially prominent in the Orchestiidea (Fig. i). In the 

 Caprellidea the first gnathopod, owing to the fusion of the first 

 segment of the thorax with the head, appears to articulate with 

 the head and to be associated with the mouth parts. 



Antenna. 



The antennae may be very long, as in the males of many 

 QEdiceridae, Phoxidae, and Lysianassidae in which they surpass 



