AMI'HIPODA OF SOUTHERN NEW ENGLAND. 461 



with the bead, but the line of union is usually clearly indicated on the outer surface. 

 The thorax is composed of seven free segments, cadi of which, except in some of the 

 Caprellidea, bears a pair of appendages. The abdomen in the typical Amphipoda 

 consists of six segments and a small terminal appendage, the telson, which perhaps 

 represents an additional segment. The segments of the abdomen are usually free, 

 but in some forms the last two ma}' be fused. In the Caprellidea the abdomen is 

 reduced to a mere rudiment. 



Eyes. — The eyes of amphipods are sessile and generally compound. In the 

 Ampeliscidae there are instead of two compound eyes usually four eyes, each with a 

 simple corneal lens. The eyes of the Hyperiidea arc frequently of enormous size, 

 covering most of the surface of the head. In Phronima they are distinctly separated 

 into upper and lower divisions. 



First mit, nnse. — The first antenna 3 are composed of a basal portion, or peduncle, 

 which never consists of more than three joints and a terminal, usually multiarticulate, 

 flagellum. A secondary flagellum is often present, but is generally of small size. 



Si '"in/ iin/f una . — The peduncle of the second antenna? consists typically of five 

 joints. In the second joint occurs the opening of the antenna! gland, which is 

 generally indicated by a conical prominence. The flagellum is generally long and 

 slender, but in some forms it is short and stout and employed in locomotion. Both 

 pairs of antennae bear setae, and often olfactory clubs and peculiar slipper-shaped 

 appendages called calceoli. 



Upper lip. — This is a plate articulated in front of the mandibles. Its form 

 varies greatly in different groups. 



Mandibles. — The mandibles of amphipods are sti - ong and adapted for cutting 

 and grinding. On the outer surface is inserted the palp, which never consists of 

 more than three joints and may be reduced to two or even one. In many forms it is 

 absent entirely. The inner edge of the mandibles is generally divided into teeth. 

 Below the principal cutting edge is usually a smaller secondary plate, which is 

 movably articulated and generally dentate. On the concave surface of the mandible 

 there is usually a large molar tubercle with a roughened, rasping surface. In some 

 forms (Lyssianassida 1 ) the molar tubercle may be small or absent. The right anil 

 left mandibles commonly differ in structure. 



Loire/' lip. — This consists of two principal lobes fused for a certain distance in 

 the middle line. 



First maxillse. — The first maxilla? consist of an inner plate, an outer plate, and 

 a palp. The inner plate is smaller than the outer and is frequently very much 

 reduced in size, or absent. The outer plate is elongated and tipped with a row of 

 stout, curved, and usually denticulated or pectinate spines, which are employed in 

 mastication. The palp consists of two joints or less. In Orchestia and some other 

 genera it is absent. 



Second maxillae. — The second maxilla? are slender and weak and consist of a 

 basal piece, upon which are joined an inner and an outer plate. These are generally 

 flexible and setose on the margins. 



MoxiUipeds. — The maxillipeds consist typically of an inner plate, an outer plate, 

 and a palp. The first joints of the right and left maxillipeds are fused in the middle 



B. B. F. 1904—30 



