1 6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



The head is always quite free from the thorax except in the 

 Caprellidea, where it is fused with the first thoracic segment. 

 It is largest in relation to the rest of the body in the Hyperiidea 

 and smallest in the Caprellidea ; it is always longer than the first 

 segment of the thorax in the Gammaridea. . 



The anterior margin of the head may be prolonged in front 

 to form a rostrum between the bases of the first antennse. 

 Usually the rostrum is an inconspicuous, pointed process, but in 

 some genera it may form a hoodlike projection over the basal 

 joints of the antennae as in Harpinia, Phoxocephalus, and Para- 

 phoxus. In Siphoncecetes the rostrum is spiniform; in 

 Dexainine and Epimeria it is curved ventrally. In the Ampelis- 

 cidae the first antennas are so closely appressed that the rostrum 

 is wanting. 



The anterior margin of the head between the bases of the 

 first and second antennae projects forward as the interantennal 

 lobe, which is usually semicircular but may be acutely pointed 

 or variously modified. In Haustorius, Sympleustes, and D ex- 

 amine, the interantennal lobes are acute. The Ampeliscidae are 

 peculiar in the great distance that separates the first and second 

 pairs of antennae and the almost complete disappearance of an 

 excavation in which the latter articulate. Usually the second 

 antennae are joined to the head only slightly posterior to the 

 first pair; but in those forms in which the second antennae are 

 more or less pediform, the front margin of the head may be 

 deeply excavated as in Ischyrocerus, Jassa, Ericthonius, Coro- 

 phium, and Unciola. 



Eyes are usually present and compound. In a few species 

 they may be lacking, as in Harpinia plumosa and Stegocephalus 

 inftatus, or imperfectly developed, as in Phoxocephalus holbolli 

 and Haustorius arenarius. In most of the CEdiceridae the eyes 

 are situated so far dorsally that they are almost in contact with 

 each other. The Hyperiidea have very large eyes that cover the 

 whole side of the head, but in the Gammaridea the eyes are never 

 very enormously developed. It is only in the Ampeliscidae that 

 we find the one pair of compound eyes generally present in the 

 Amphipoda replaced by two pairs of eyes provided with simple 

 corneal lenses. 



